People usually say that the main difference between depression and sadness is that depression:

A: Happens for no reason, even if everything in your life is fine, you still feel like shit

B: Happens for a way longer period of time compared to sadness

This sounds about right, right? Bullshit. The problem with A, is that a lot of the time there is a reason that someone is depressed, but they have not yet found the underlying cause, so they label it depression and just call it a day. This is not how it should be. I need you to know that there is always a reason why you feel like shit everyday, and for a lot of people it's hypothyroidism. A thyroid condition is strongly correlated with feeling depressed for "no reason", I even see a lot of people here saying things like "I feel so cold" "i keep gaining weight" "i'm always tired" these are all symptoms of hypothyroidism, and depression is a symptom of hypothyroidism.

Food intolerances aswell, gluten and dairy can cause you to be depressed for seemingly "no reason", but it may just be a food intolerance. Vitamin deficiency, especially B1, can trigger depression, and even sleeping pills like melatonin, can trigger depression as a side effect and cause a random depression to pop out of nowhere, as people like to call it, it's not random at all. There is a cause. Stop saying you just have depression and it happened for no reason, you don't just "have it".