I thought I'd recount an anecdote from the other Saturday when the Brinkster Clan were returning from shopping on the Purley Way (Croydon, for the uninitiated).
Driving back across Mitcham Common traffic was moving very slowly in stops and starts for no readily apparent reason. Normally it's not too bad so this was unusual but eventually it stopped entirely. I could see about 5 cars in front of me but then my view was blocked by a white transit so we waited and waited. After about 3 or 4 minutes of not moving I edged the car out and saw that in front of the Transit was entirely clear road. Huh? A couple of others behind me noticed it too and we pulled out and whizzed past the other sheeple still queuing patiently.
It was as we passed the transit that we noticed that the driver was slumped over the steering wheel, held up by his seatbelt, so I quickly pulled over to the side and ran back to see what was happening. As I got to the drivers door he was still slumped down and I could see his face looked pretty grey so I banged on the driver's door window to see if I could get a response. To my (and his) great surprise he sat bolt upright, staring at me in complete shock with his bloodshot eyes wide with fright. He turned and looked at the empty road in front of him, threw it into gear and drove off.
I can only assume that because of the slow moving traffic he'd dropped off to sleep.... which was a lot easier to explain to the Clan than about him dropping dead. Almost gave me a heart attack though.