I've got the exact same problem. Sometimes I can play for several hours and sometimes it happens after about 30 minutes of play.
I get a message about graphics card drivers crashing, something, something. There is never time to read the whole message as it disappears instantly as you tab out of the game.

This just happened to me as well. It was just after a server restart at the small military base south of the NW air field. I was running away from a zombie and equipping my fire axe when I got the black "you are dead" screen.

I am absolutely sure that I had 100% health as I had the green energized, hydrated and healthy buffs (and had just finished healing about 10 min prior to server restart). I could see my surroundings in full color and had no reason to believe anything was wrong with my characters health.
Also I have noticed that the U.K Assault vest seem to get ruined after one hit from a zombie, and in about 25% of the times, all the stuff you keep in it gets ruined as well. I understand that it takes most of the damage most of the times but its the "all or nothing" that makes me wounder if its supposed to be this way?