This question is worth answering directly: if you are asking it, the answer is almost certainly not laziness.
Laziness, in the common sense of the word, is a preference for ease over effort. People who are lazy do not tend to suffer for it. They do not feel guilty about resting. They do not spend energy worrying about whether they should be doing more. The fact that you are searching for an explanation, and that the explanation you have arrived at is something negative about yourself, is itself a signal worth paying attention to.
What depression looks like from the inside
One of depression’s more destructive features is that it is often interpreted by the person experiencing it as a moral failing. You should be able to push through. You should want to do things. You should be able to concentrate, keep up with your responsibilities, engage with the people around you. The gap between what you feel capable of and what you think you should be capable of generates shame, and shame tends to make depression worse.
The NHS describes a loss of motivation and energy as a core symptom of depression, not a character trait. The brain systems responsible for motivation and drive are directly affected by depression. When those systems are not functioning normally, effort feels much harder than it is for someone whose brain is working differently, and there is a neurological reason for that, not a moral one.
The difference in how it feels
Laziness, to the extent it exists as a meaningful concept, tends to feel comfortable. Depression does not. Depression feels like effort without reward: you cannot do the things you want to do, and the inability itself causes distress. If you have been feeling guilty, frustrated with yourself, or genuinely puzzled about why you cannot seem to function the way you used to, that pattern is closer to depression than to laziness.
You might also find it useful to read how do I know if I am depressed or just going through a hard time? and why can I not concentrate on anything any more?
The PHQ-9 cuts through the noise
The PHQ-9 asks whether, in the past two weeks, you have been bothered by feeling tired or having little energy, by moving or speaking more slowly than usual, or by little interest or pleasure in doing things. These are not questions about motivation in an abstract sense. They are questions about specific, measurable changes in how you are functioning.
If your score comes back in the mild-to-moderate range, that is useful information. It means there is likely something worth treating, and the treatment works.
What to do
Mind has a clear explanation of how depression differs from ordinary low motivation. The Mental Health Foundation also has accessible information.
If you want to try something practical, Beside is a free five-week programme over WhatsApp. No diagnosis required, no referral, no waiting list. It is built for people who are struggling to function at their usual level and want structured support. You do not need to have resolved the question of whether this is depression or something else before starting. Sign up here.