Above the Armstrong limit you're looking at 9-15 seconds of useful consciousness. (The time you are conscious enough to take actions to save yourself.)

When a deep sub implodes you're going to be hit by water moving at the speed of sound in said water (1,500m/s, considerably faster than in air.) That's far above the speed of nerve impulses, there's no way a pain signal could reach the brain before there isn't a brain left to get the signal.