The pixel art overall is pretty good. the animation on the other hand is not that good. This little monkey is going to fall unconscious of hyperventilation at any moment!
You move the shape too much, and too fast. I would advise you tu use sub pixel animation for this kind of subtle animation. You move the shape wayyyy less and instead move pixels inside the shape to create the illusion of motion. I made a crappy edit to demonstrate my point:
Imagine the same thing with twice as much frames, you can give a fluid, subtle breathe idle animation without moving the shape more than one single pixel.
Hope it helps, try it for yourself! Also, post images at 100% the size, don't up-scale them, it only forces people who want to edit them to rescale them. You can just click on any picture posted here to zoom in.