Not everyone that excessively speeds or drives recklessly will look at the scene of a crash and be shaken by it. Some might even be like at least I wont feel it.....

Scary thought tho.... We cant ask those that died instantly if they felt it or not. For all we know they might. Probably not but again cant ask. But I do know one explosion survivor was able to describe how the Shockwave felt as the air was vibrating thier body like being between two metal plates vibrating like a ringing metal bat but far worse feeling. So the brain or something processed fast enough to let them feel that. So. Who knows if instant is really painless....