Walking helped me sleep only because the sun exposure was good for my circadian rhythm. Right now it's too cold here to go out so I've been using the elliptical I just bought. The nice thing about it is you can exercise far harder than walking without feeling anywhere near the exertion you would get from running. I don't miss the car exhaust, or walking to the point of getting half dollar sized blisters on my feet, either.

I tend to use it on high resistance and incline, to the point I'm dripping sweat by half a mile, and it seems when I hit 1.5 miles or more in one day (no matter how many breaks) the amount of sleep I get is strongly affected but I still wake feeling energized. My mood has been pretty good bordering on hypo since I did 2.8 miles in one day last week.

All-out sprinting and heavy weight lifting are the only things that drain my energy; mild to moderate cardio actually amp me way up. I'm not sure how exercise affects me depending on my mood, as I only seem to get bipolar episodes every few years, and everyday between them is like a mini roller coaster that I can manage reasonably well without treatment.