I’ve had several stretches of depression in my life and they are usually marked by a restless, anxious, gnawing, dark, aimless energy and an inability to sleep well or settle down and concentrate. I also tend to withdraw from interactions that require negotiating with people I don’t know (including simple things like making care tune-up appointments).
I’m really good at faking that I’m okay to everyone but the two or three people closest to me. When I’ve hit really rough spots I have actually wished that it was in my psychological makeup to say “screw it” and lie in bed for days until someone hospitalized me. Unfortunately, I’m a control freak and can’t even let go when I’m in acute distress. This last year has been the most difficult year of my life and very few people know this (well, now the 20 million people on SDMB know)
Ditto previous posters on the feeling that when major depression hits it often seems that it wouldn’t matter to anyone if you were to just disappear from the world.
I think I am fortunate in that when I hit late 20s I started to feel much better for longer stretches. Now depression seems to be more situational and related to events like death, major change and loss, etc . . .