[Despare]

Well, on my server, I'm making has a problem that I don't know how to fix. Well, the problem is when I am messing around in my server, the health of the player goes down slowly 1 by 1. How could I fix that? and how could I make it so when you log off and then log back in, you have the health you last logged off with?
Your help would be really appreciated, Thanks.