When I was overseas I used to constantly have a dream where the bullets were so slow you could see them and they would bounce off the bad guys. Then my M-16 would hopelessly jam and I would be overrun while trying to clear it. I would punch the attackers, but my motions were incredibly slow and had no affect, and then I would wake up as I was about to be killed.
It turns out these dreams are extremely common among deployed armed forces and other armed professionals. The advice I was given was when you wake up, re-imagine the scenario but with a positive ending. Your gun works like it should, you hit your attacker, the attack stops. Then go back to sleep. It becomes less rattling and even decreases the occurrence rate of such dreams. It worked for me.