Hmmm....are you sure he is napping or is he laying on the bottom because there is something wrong with him?? I have 3 fish tanks and during the day when the lights are on none of my fish are "napping", they're always being active and swimming around, including my Malawi cichlid tank. Usually, if I see one of my fish laying on the gravel, that kinda puts up a red flag for me, like something is not normal. I could be wrong though, maybe Acaras do nap?? 
