How do you know for sure you're depressed? What does it feel like?

I always thought of depressed people as permanently sad, sad-sad. I thought it was brain chemical and not situational, such as going through changes, having adjustment problems, or having low confidence and not realizing that there’s a choice to move forward, to turn things around, or to make bold changes. In other words, depression seemed to be something that if one had it, one would know it. It would be so obvious.

..not sure if I understood it correctly.

Back in college I had sessions with a college shrink. I went to see him only because I didn’t think I was coping well. Didn’t stick around long enough to learn anything. I only remembered that in college I rarely laughed, at occasions spoke in monotone, did not understand “normal people” my age, was annoyed by their enthusiasm, etc. The shrink asked me what I did for fun; I told him I didn’t really do anything for “fun.” My appetite was normal.

Even as a kid, at times I felt bored and meaningless and pessimistic. While my brother shared with me his dreams of doing this and that, I, as a kid, would tell him not to dream too much. I didn’t want him to have hopes; I feared that he would be disappointed. My “normal” could mean neutral or a little sad. Sometimes I realized I could be out there, letting myself go, though that seemed phony because I didn’t think it was going to last anyway.

Me today: I think happiness is a state which, if desired, you constantly create a condition for it to happen. It’s something you maintain. For example, eat well, drink water, exercise, get sunlight, maintain positive thinking, socialize sometimes, etc. The mundane.

I wonder: What would a real depressed person look like? What would it feel like? Are you super sad and all the time? How do you know for sure that you’re depressed, like your brain’s wiring is off, or that you’re just a tad bit on the sad/realistic side?