Disconnected from server when doing pvp

I'd recommend doing a manual Login in this case. Properly log off from the game, using the Logout button in the games Info box, then sign into the game with your credentials. Please tell me if that worked for you. Clearing Browsercache & Cookies is also useful in that case.

The same thing has happened to me sometimes in several worlds after long time connected.
The recommendation to close session and re-enter before starting any combat is very good.