I have also had a problem like this...
I ran out of spawn and made it to a building on the new map, then i was back in the woods i ran through about 15 seconds ago. When i got to the building i started to die, it was as if my body was still at spawn and someone was hitting me. No health was being removed from my health bar but a few seconds later i died. Also after this i could not respawn.
My minecraft runs fine, i was on the right EU server, i have optifine and my setting were on low. I dont think this is to do with my client