It's a little unusual, they generally roll up the tail while sleeping and make themselves as small as possible. could be its caught active when the lights go out?
Does the room go from light to total darkness? Try leaving a dim lamp on after lights out for 20 mins, see if it doesn't find a more natural sleeping position.
I have my tortoise in the same room. Chams lights go off first, 5 min later torts lights go off. Gives him a little time to find a spot if he needs it but he's already "in bed" before his lights turn off anyway, he's got it down. But that's an idea if you have another animal that uses lights.
How long have you had him? My veiled slept upside down hanging from the top of his cage for the first two nights. I checked on him all night, in fear he would fall but he hung there til lights went back on??
Maybe try moving a vine there. Maybe that is his favorite spot for the warmth or night chill but there is no where to put his feet. Put a branch or vine and see if he will move to it. It's worth a shot