By the time you ducked from the shots and figured out what was going on it would be over.
Anything else is foolishness. You'll never know what's happening until well after it's over.
Realistically this is how things would happen.
GUNFIRE, freeze like deer in headlights, wake up to the presence of the Ghost of Mr. Darwin, seek cover, seek escape, contact 911, beg for help, changer underwear.
No body's shooting back at anyone unless things go on for a very long time and/or someone leaves the vehicle to start shooting people that have taken cover.