Stress
Interview with a tanker of WWII
Tanks of WWII were largely blind to small troop movement, and an unsupported tank could be overun relatively easily. Before the invasion of Normandy, .50cal MGs were removed from the outside of the tank to prevent them being used by German troops. "And hell, if the tank got hit, you didn't know if you were gonna open the door or not, because the gun might have been over it."
The guns of the Tiger tank were easily a match for most Shermans fielded by the Americans, and a near miss would scare any tanker of M4 Shermans. Shermans were famous for being extremely flammable due to using high-octane fuel as opposed to the more stable diesel fuel. "I leaned over on the tank with my hand, and in that shroud that comes up just below the end of the tank, there was a big hole. That 88 went clear through it."
http://www.tankbooks.com/amile/bussell/bussell.htm
The stress caused in the interviewee is specifically fear-induced stress, fear for his life. His adrenal glands pumped epiniphrine and other hormones into his system, inducing a hightened state of awareness, shaking of his limbs, and a strong urge to fight or flee.