Game Becomes Unplayable

This is the second game in a row where about twenty minutes into the game whenever I click it pings and if I press enter, the game window changes from full screen to a window screen. And I pretty much can't do anything and am forced to quit. If I try to close my client to restart it, it doesn't let me rejoin the game. I don't know if other people are getting this but it's getting very frustrating.