Dead ball when injury strikes

Interesting to see that when ten doeschate was sadly injured in the Somerset v Essex Twenty20 match last night, Somerset threw the ball in to the bowler's end as he hobbled towards that end, but Pollard fumbled badly, allowing ten doeschate to make his ground and then collapse in agony. The umpires called dead ball I gather (correct me if I'm wrong!) and the ball was replayed after ten doeschate had hobbled off.

My question for umpires out there is what defines the call of dead ball? I can forsee a situation where someone slips and stays down knowing they will probably be run out, and is then fit to carry on after a short period of fake hobbling....