To my knowledge, this is quite normal. I've raised a few buns and seen this a lot. I have a bun who sits up and sways a bit before falling asleep. I would suggest letting him out of the cage, buns need lots and lots of exercise and can get really bored in cages.
Bunnies can really come to life outside of their cages, and when they feel safe are so affectionate, so if hes just sitting there most of the time, then he's probably very bored.