I died when i rejoin my world

I am not sure what version i selected, but just in cashe, current version is 1.8.1. Let me explain what happens:

 

1. I join my world and i just died
2. I save and exit the world
3. I joined another world
4. Wait for a bit
5. Rejoin back again
6. Died

I am not sure how i died, but my difficulty world is hard. When i put back to normal, nothing happens.