It's not that hard to get up... So long as you don't mind an awful lot of internal bleeding and some crushed ribs and the like. Unless the hammer hits you square in the head in which case you're dead before you finish the thought you were thinking.... (j/k)
Sledge hammers do indeed bloody hurt... And I've only ever felt one hit me from the front with little momentum. If I was lying on the ground and one started coming down....
Death is the only thing I foresee there.

Anyway, our clubs sort of stagnant at the moment...
Can anyone think up another good topic?