I did overnights for about three months to fill in stocking at a grocery store. I actually really enjoyed the shift, but I think it was because I was working 10-12 hour shifts (8pm until 6-8am) and had a lot of free time otherwise. I had a problem sleeping during the summer with the daytime heat pouring in and no a/c (not possible in that room). I was ok staying up during the day if I needed to. I do remember an emergency that really stressed me out one morning and while riding with my mom in the car, I fell asleep while dialing a number in the cell phone. That really scared me.
I also lost a lot (I mean a lot) of weight working overnights, I'm not sure why.