Yeah they are called flashbacks.

I find when i have flashbacks is related to how stressed i am and they can be totally disabling. Whats worse is when it turns into a hallucination and you react physically to the hallucination. When you come back to reality after shouting you feel really embarrased if someone else sees you and looks at you like your nuts!!!

The ones i really hate are the short flashbacks, only a second or two where in my case id see an armed man who doesnt exist Makes you shit yourself like Or another one i get is i relive getting splattered in blood and that burning flesh smell. Can be walking along and I get the feeling on my face and the horrible smell!