For me it's not so out of the blue. I'll be in a really wired state (wired, not weird), trying to learn and do as much as I can, but somehow I end up getting disappointed when I don't achieve what I'm trying to, or realizing that it will take too much time that I don't really have. So that might just be a natural reaction to the situation. But I don't stay down for too long. I usually immerse myself in something else the next day, and then get disappointed again. When I'm in this state I'm prone to anger, agitation, and overreacting. I also get a really tired and then wired cycle. Tired in during the latter part of the day, and then wired at night, to the point where I need to knock myself out with a heavy dose of benzos. In my case it might be just flat out hypomania/mania. I don't get really bummed out. I dunno. I think a mix state would have more severe lows than what I get. But this state has been persistent since last July, though the first few weeks I was really, really wired. Now it's steadily on the high-side, but close enough to where a trigger could knock me over the fence into "highly-regrettable behavior and actions land."

When I get depressed I tend to stay down for quite a while, several weeks or more.