Sleeping beta?

Does anyone else have a fish that sleep on the bottom of the tank, on their stomach?
Ive had my beta for a few months and hes in great health and very active during the day. When i turn the lights out at night, he goes to sleep and settles on the bottom to do so. If i turn the lights back on he perks back up again. Does anyone else have a fish like this??

I brought him home for winter break (i live at college) and my mom told me she thought he was dead when she saw him this morning, resting at the bottom. I told her he does that every night and not to worry, hes just sleeping but she said that shes never seen a fish do that before.