I think both. In my situation it is primarily situational, but the chemical whosey-whatsis in my brain does not handle things well. Wires just get crossed in my head. I avoided meds for years thinking that "things just weren't that bad" and I could get over it on my own. (This belief is a learned behavior from my childhood, and how I compensate for the craziness around me -- "I'll do it myself".)

So I'm on a low dose of antidepressant that takes the edge off. But I still crash (like yesterday), putting too much pressure on myself. Even knowing that does not alleviate the depression ...it now seems physiological in me. Sore shoulders, OCD thoughts. I'd say try to consider it is both elements, and not just you changing your life.