When I'm sleep deprived, a little white cat darts across the room in front of me. I've seen ghost-cat in night clubs, at work, at home... It's freaky.
It's a real and serious issue. I don't care how many in here think they are RAMBO the human body and mind in each individual has specific limits. The brain in an act of self preservation can and will shut done if too many of it's limits are exceeded. It will be involuntary and the person can not do one thing to stop it.
Sad to say human physchology and the human brain are for the most part not open too dicsussion nor in many venues taken seriously in the military depite the fact that understanding it and using it may save many of our troops lives both on the battlefield and after. The one place I know of where it is taken deadly serious is The Navy submarine fleet. The officers and senior NCO's watch close for problems.