There is robin on the ground holding it's tail feathers in the air (it's cold and drizzling outside) shaking?

I went out to check on it...it's puffing itself up and shaking. It made a feeble attempt to hop away from me...just a couple steps. It had three little piles of bird poo under where it had been on my sidewalk. The next time I got closer, it did like a weird/low/sideways fly over into my mulch. It layed there on it's side, but shortly after kinda stood up, lifted it's tail feathers up and is shaking periodically...looks almost seizure like. I feel like it's dying, but not sure. Poor thing. Any ideas from the bird people out there? I hope no cats come around it.