Depression that ends instantly for no reason?

I was depressed all week, and it was especially debilitating this morning (Thursday). It was like a fog in my brain where I couldn't make even the simplest decisions like what to eat for breakfast. I knew that exercise might help, but I felt so tired and all I wanted to do was find a dark place to curl up and sleep. I spent most of the morning slumped over at my desk.

Then *poof* it's all gone, and I feel normal this afternoon. The change happened for no apparent reason in less than 10 minutes like something was clogged in my brain and suddenly became unclogged. I've noticed this before where the depression gets worse and worse over several days and then suddenly vanishes in an instant.

Has anybody else experienced this? I'm curious because I know the way I experience depression is different from most people. Maybe if I knew more about my problem then I could handle it better.

Maybe you could identify the reason for your sudden attack . Like sometimes, when I have worked a lot( like I am over-worked and haven't had a decent break) and I am very stressed out, I tend to get really, really depressed but only when I start to relax. Then I get depressed and I just lie down; I can't get up. I want to kill myself or faint or something, so that I don't feel what I feel.
Well, I tend to hit rock bottom after I have slept and relaxed; it is not like these feelings hit me immediately after I am done with something stressful. It is probably because I am burnt out; my feelings have just started to catch up with my body maybe. Maybe, when I was really stressed out, I was benumbed by the stress to the feelings accumulating within me. Then when I am on break, they are released. I don't know but that's what I think it is. Since this happens every time I am over-worked.
But then after a while, when I just sit still or don't do anything, I start to feel better, immediately after the next day.
This is different from the regular every day, prolonged feelings of depression I have. These feelings are very sharp and acute and intense. So for me these short attacks probably have little to do with the external reasons for my every day depression.