I didn't see a report for this bug so here it is. I have a pen of sheep and a pen cows. When I go inside either of them, colliding with the mobs sends me the opposite way at an extreme pace. Re-logging only works for a little while. I think this also happens with some other mobs, because I've had them dropped on me by my mob farm. I've been try to recreate this bug in a test world for a while with no success. At this point I think this may just be a fluke glitch in my world.

I'm not sure why but it's been fixed. The bug is resolved, please close this ticket.