There are as many possible answers to this question as there are people, so it will be difficult for you to determine which perspective makes the most sense to you.
Depression is so common that more than half of the world’s population will experience it at least once in a lifetime.
There are advantages and disadvantages to seeing depression as a chemical imbalance which needs to be treated with medicine or less imaginative, old-fashioned therapies. It is based on the medical paradigm, a framework the is often also used to explain and treat psychological conditions.
If I were suffering from depression – which I might have, but I was never diagnosed as such – I would avoid that framework. I read a very convincing article of some professionals explaining depression not as an illness, but rather as a different way of experiencing, allowing to make more difficult decisions with the kind of cognitive reasoning that often works better when in a depressive type of condition.
Maybe my words do not fully reflect the authors’ findings and views, but I really do believe and have experienced that depression allows one to process difficult life questions and situations more effectively.
But of course you do not want to be a cognitive processing machine that is unable to enjoy life. That’s why I prefer to explain depression as letting your “thinking self” rule your experiences. At your core, you are NOT a thinker. You are a neutral consciousness experiencing sensations that, by your “thinking self” get labels and that’s when the trouble starts. Delusional ideas like “past”, “future”, “good” and “bad” are starting to appear out of nowhere and even though the world at its deepest level does not appear to fit those labels, you still believe them. Labels, even positive ones, eventually limit, harm and imprison you. This actually applies to both depressed and non-depressed people.
The only way to break free is to accept and experience everything without labels and values and feel our innermost core, which is always living in the present – as past and future are only constructions of the “thinking self”.
This is why mindfulness approaches – and by extension, Buddhism, where that idea originally comes from – seem to be so effective and popular.
But the popular derivatives of the experience of the present only bring you so far, they do not fully free you from struggling with your “thinking self”. For real freedom, you must be willing to sacrifice ALL your values, labels, conceptions and ideas.