Is a five hour nap still considered a nap?

I got home from my lab today, and after being tired all day, decided that a short nap was in order. I was thinking maybe half an hour. Apparently my body was thinking a little more than half an hour, because I didn't stir until 10pm, five hours after I began this "short nap". Now it's 1:30 am, and I'm not the least bit tired. Blah. Well, I think I may as well just lie down until I fall asleep...good night!