There's lots of really good advice out there about how to cope with flashbacks.
Trouble is, it doesn't really work. Because when you are in the middle of a flashback, usually on your own, the thoughts that come to mind are not, "Oh, I should stamp my feet / remind myself this is not happening now / notice what I can see." When you are in a flashback, you are in a flashback. Not outside it, watching what is going on. You are there, in it, experiencing it. Or at least, that's how it is for me.