main thing that's throwing me off is the pin wheel, you've got it jumping forward an extra 90 degrees in some frames.
it's proportions look a bit inconsistent as it spins, a little tough to perfect, but worth the extra effort.
I too would suggest some extra frames of detail for his breathing/tail etc
here's the old mario sleeping scene from SM2 (couldn't find the snes/gba remake version animated)

it's animated pretty nicely for a NES game, a little organically, not just moving lines up and down
and maybe have it's ear twitch? my cats do that usually