Have you been feeling lately like something's just “off”? Maybe you can't sleep, can't eat, can't concentrate — yet you can't quite put your finger on what the problem actually is.
You might not be ill. But what you're feeling does have a name.
Anxiety, depression and stress — three words that constantly get talked about as if they were one. “I'm under so much stress,” “I'm so anxious,” “I just can't feel happy” — in everyday speech, they're almost interchangeable. But psychologically, these three states work in completely different ways, and telling them apart is the first step in looking after yourself.
Why are they so easy to confuse?
Because they really do overlap.
The psychologists Clark and Watson (1991) proposed a “tripartite model” to explain the relationship between anxiety and depression. They found that the two states share one core component — negative affect — that diffuse sense of being uncomfortable, unhappy, ill at ease in your own skin.
This is why you might find yourself thinking, “I can't tell whether I'm anxious or depressed” — because the underlying tone is the same.
But Clark and Watson also pointed out that each has its own distinctive component. Anxiety is marked by physiological over-arousal — a racing heart, trembling hands, shallow rapid breathing. Depression is marked by the loss of positive emotion — being unable to summon any enthusiasm for things you once enjoyed, no longer feeling any joy.
Lovibond and Lovibond (1995) later developed the DASS scale (the short form, DASS-21, has 21 items), which sets out to measure all three dimensions — depression, anxiety and stress — within a single questionnaire. The very design of the scale reflects an important point: although these three states are related, they can be identified separately.
Stress: it has a target, and a deadline
Stress is the most “normal” of the three. It's your response to an external challenge — a deadline, an exam, a clash with someone, a house move.
The hallmark of stress is agitation and tension. You snap easily, find it hard to relax, and feel as though you're being pushed along. That's precisely what the stress subscale of the DASS-21 measures: difficulty relaxing, nervous tension, being easily upset, irritability and a lack of patience (Lovibond & Lovibond, 1995).
The key is this: stress usually has a clear source. Once the deadline passes, the stress eases. Once the exam is over, you breathe out. Stress is a response with a “target” — and when the source of stress disappears, the symptoms usually fade with it.
But what if the source of stress doesn't disappear?
A literature review by Ross, Foster and Ionescu (2017) points out that long-term stress alters the brain's stress-response system. According to existing research, more than 55% of people with depression have elevated levels of cortisol (the stress hormone) in their bodies. The available evidence suggests that in people who spend a prolonged period in a high-stress state, the brain circuits responsible for reward and threat responses may change — put simply, your brain gradually learns to stay “on permanent standby,” until it can no longer muster any enthusiasm at all.
This is one possible mechanism by which stress may come to be linked with anxiety or depression.
Anxiety: the threat is already gone, but your body doesn't know it
Anxiety and stress look very alike, but there's one key difference: anxiety often has no clear target.
Stress is “I have to hand in a report next week, and I'm so tense.” Anxiety is “I've handed in the report, and I still feel as though something's going to go wrong.”
At the heart of anxiety is worry about the future. Your mind plays the “what if…?” reel on a loop: What if I'm not good enough? What if they don't like me? What if something goes wrong? This kind of worry doesn't need any basis in reality — it grows all by itself.
At the bodily level, anxiety shows up as what Clark and Watson (1991) called “physiological over-arousal” — a racing heart, tight muscles, difficulty breathing, sweating. Your body seems to detect a threat even when your rational mind is telling you there's nothing wrong.
This is exactly what the anxiety subscale of the DASS-21 captures: the body's automatic responses (racing heart, dry mouth, difficulty breathing), trembling, and a sense of dread for no reason at all (Lovibond & Lovibond, 1995).
It's worth noting that the comorbidity rate of anxiety and depression is extremely high. Zbozinek et al. (2012) analysed data from 1,218 primary care patients and found that four symptoms overlap across the diagnostic criteria for generalised anxiety disorder (GAD) and major depressive disorder (MDD): difficulty sleeping, restlessness, fatigue and difficulty concentrating. Among patients who met the criteria for both diagnoses, the average endorsement rate for these four overlapping symptoms was 90.6%.
This means that if you have all four of these symptoms at once, the symptoms alone make it very hard to judge whether you're “anxious or depressed” — because the answer may well be both.
Depression: not “feeling down,” but “feeling nothing”
A lot of people think depression is simply being “heartbroken.” But a more accurate description is: feeling nothing at all.
Clark and Watson's (1991) tripartite model points out that depression's most distinctive feature isn't sadness, but a lack of positive emotion (low positive affect). It's not just that you're unhappy — it's that you've lost the capacity to be happy. The things you used to enjoy no longer draw you in, seeing friends feels exhausting, and even sitting down to a good meal feels like it's “not worth the bother.”
What the depression subscale of the DASS-21 measures includes: feeling that life is hopeless, thinking little of yourself, having no interest in anything, no longer feeling any joy, and being unable to work up the enthusiasm to do anything (Lovibond & Lovibond, 1995).
Unlike stress and anxiety, the time dimension matters a great deal with depression. Stress usually tracks events, anxiety may come and go, but depression is marked by persistence. Clinically, a diagnosis of depression requires the symptoms to last at least two weeks and to interfere with daily functioning.
Another important distinction is the direction of energy. Anxiety is a high-energy state — your body is constantly “doing something,” it's just that what it's doing is worrying. Depression is a low-energy state — your body is as if switched off, without even the strength to worry.
How can you tell which state you're in?
This isn't about diagnosing yourself. But a few questions can help you sort through your thoughts:
“Does my discomfort have a clear source?” If it does — say, work stress, relationship problems, financial difficulty — and you feel that “if only this one thing were sorted out, I'd be fine,” then it's more likely to be a stress response.
“Is my body over-reacting?” A racing heart, trembling hands, rapid breathing, tight muscles — and these reactions are out of all proportion to any actual threat? That looks more like anxiety.
“Have I lost the capacity to feel happy?” Not just “feeling down,” but unable to summon any enthusiasm for anything, with a sense that nothing really matters? That looks more like a feature of depression.
“How long has this state lasted?” Stress usually fades along with the event. If your symptoms have lasted more than two weeks and are increasingly disrupting your daily life, then whether it's anxiety or depression, it's worth taking seriously.
But bear this in mind: according to data from the US National Comorbidity Survey, 67% of people with generalised anxiety disorder have also experienced depression at some point in their lives (Judd et al., 1998). These three states aren't an either/or — they often appear together and intensify one another. Telling them apart isn't about pinning on a label; it's about knowing what you can do next.
In closing
By the time you've finished reading this article, you may have realised that what you feel doesn't fit neatly into just one category. That's perfectly normal. In real life, stress, anxiety and depression are often woven together, with blurred boundaries.
But one thing is clear: being able to name your own experience is, in itself, a kind of strength. The moment you can say “I'm not under a lot of stress right now — I might be anxious” or “I'm not just tired, I might need some help,” you already understand yourself better than you did yesterday.
And once you understand the state you're in, the most important next step isn't to keep searching the internet for answers.
Not sure whether it's anxiety or depression? You can talk it through with a psychologist
If you've already tried to handle it on your own but the symptoms have lasted more than two weeks, or you've noticed your daily life starting to suffer — you can't get out of bed, you can't focus, you've lost interest in everything — it may be time to talk to a professional.
TreeholeHK's clinical psychologists will first help you get clear on the state you're in, and then work out the next step that's right for you, together.
What's the difference between anxiety and depression?
According to the tripartite model proposed by the psychologists Clark and Watson (1991), the core feature of anxiety is physiological over-arousal (such as a racing heart and rapid breathing), while the core feature of depression is a lack of positive emotion — being unable to summon any enthusiasm for things you once enjoyed. Both involve negative affect, which is why they're so often confused.
What's the difference between stress and anxiety?
Stress usually has a clear external source (such as work or exams), and when the source of stress disappears, the symptoms usually fade with it. Anxiety, on the other hand, is the persistence of worry and bodily tension even when there's no clear threat. The psychology literature widely notes that stress is a response to a situation, while anxiety is a response to stress — even when the source of stress disappears, anxiety may still persist.
Can anxiety and depression occur at the same time?
Yes, and very commonly so. According to data from the US National Comorbidity Survey, 67% of people with generalised anxiety disorder have also experienced depression at some point in their lives. The two share four overlapping symptoms across the diagnostic criteria: difficulty sleeping, fatigue, difficulty concentrating and restlessness.
Can stress turn into depression if it lasts too long?
It's possible. A literature review by Ross et al. (2017) points out that long-term stress alters the brain's stress-response system, and more than 55% of people with depression have elevated levels of cortisol (the stress hormone) in their bodies. Persistent stress may be linked to a condition known as “anxious depression,” a subtype whose treatment response differs from that of ordinary depression.
When should I seek professional help?
If your symptoms have lasted more than two weeks and are starting to affect your daily life — work, relationships, sleep — then it's worth considering a professional assessment. Whether your distress looks more like anxiety, depression or stress, a psychotherapist can help you get clear on your state and work out what to do, together.
Key takeaways
Stress has a target, anxiety has no boundary, depression is the loss of the capacity to feel — and although the three often appear together, telling them apart can help you know what you need. If your state has lasted more than two weeks and is increasingly disrupting your life, the most useful next step isn't to keep analysing yourself, but to let a professional help you see the whole picture.
References
Ali, A. M., Alkhamees, A. A., Hori, H., Kim, Y., & Kunugi, H. (2021). The Depression Anxiety Stress Scale 21: Development and validation of the Depression Anxiety Stress Scale 8-Item in psychiatric patients and the general public for easier mental health measurement in a post COVID-19 world. International Journal of Environmental Research and Public Health, 18(19), 10142. https://doi.org/10.3390/ijerph181910142
Clark, L. A., & Watson, D. (1991). Tripartite model of anxiety and depression: Psychometric evidence and taxonomic implications. Journal of Abnormal Psychology, 100(3), 316–336. https://doi.org/10.1037/0021-843X.100.3.316
Kessler, R. C., DuPont, R. L., Berglund, P., & Wittchen, H.-U. (1999). Impairment in pure and comorbid generalized anxiety disorder and major depression at 12 months in two national surveys. American Journal of Psychiatry, 156(12), 1915–1923. https://doi.org/10.1176/ajp.156.12.1915
Lovibond, S. H., & Lovibond, P. F. (1995). Manual for the Depression Anxiety Stress Scales (2nd ed.). Psychology Foundation of Australia.
Ross, R. A., Foster, S. L., & Ionescu, D. F. (2017). The role of chronic stress in anxious depression. Chronic Stress, 1, 2470547016689472. https://doi.org/10.1177/2470547016689472
Zbozinek, T. D., Rose, R. D., Wolitzky-Taylor, K. B., Sherbourne, C., Sullivan, G., Stein, M. B., Roy-Byrne, P. P., & Craske, M. G. (2012). Diagnostic overlap of generalized anxiety disorder and major depressive disorder in a primary care sample. Depression and Anxiety, 29(12), 1065–1071. https://doi.org/10.1002/da.22026
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