-No sleep, or very little sleep, and not missing it.
-Taking on more projects than I can reasonably handle.
-Having a totally overinflated estimation of my ability to do things, or blowing something that's normally a minor interest into an obsession.
-Occasionally I will "invest" (read: spend a lot of money) in one of those projects for a reason that at the time seems totally rational. Or, you know, sometimes I'll just spend money on something because I decide I have to have it right that second. In every color available.
-My tact filters and social inhibitions go away, and with them my anxiety in dealing with people (which is usually horrendous). I want to be the center of attention all the time, to the point of being completely inappropriate about it. I seriously feel like I can get away with anything.
-It's... really REALLY easy to get angry, and it's very sudden when it happens.
-I've been told I talk too fast and too loud as well, though I'm not the best judge of that.

This usually lasts a couple of weeks before the actual mania sets in, and the anxiety comes back. Not fun. ...Well, the hypomania is fun, I get quite a bit accomplished. My boyfriend is very good about making sure I can't get myself in too much trouble, thankfully.