A situation like this happened to me in January, and I've had many emergency/immediate decision situations happen.
One night in January, I pulled in to get gas, and I saw a police car coming with lights on, and barely could hear the siren. It was at a blind corner, and I saw a little black sedan coming at full speed from the crossroad. I knew after a split second that there was no way they'd avoid hitting, and CRASH! Neither car had a chance to even let go of the gas. There was a teenage boy driving the little black car, and he got out immediately, but the sheriff's deputy was stuck in his car, which was smoking inside & out; ready to catch fire. I hesitated for maybe 5 seconds, then I ran out in the highway (as did another man who works at the gas station). He and I forced the deputy's car open, which wasn't easy since the whole front of the car was folded to the left. Both the gas station guy and I, are pretty big, so we were able to rip the door open. (I tore a tendon in my wrist though). The deputy got out, and staggered away from the car. He was very confused and dazed, and I wasn't sure if I should reach out and give him an arm, or if he might be confused enough to think I was trying for his gun or something. I handed him his radio, and he called in for help. In a matter of minutes, there must have been 50 police cars and fire engines there. And I was in the middle of all of it, and my heart was pounding, as I HATE publicity and being the focus. I had to stay there for an hour, and be interviewed by the CA Highway Patrol, and senior members of the Sheriff's Dept. A month later, I had to go downtown and be interviewed again by the Sheriff's Internal Affairs office. I really, REALLY felt as if I wasn't being believed, as my Asperger's was in full gear under that pressure.
Nevertheless, I did it, and all is OK now. I probably will wind up in court at some time, since the kid is suing the County of Ventura, and I'm the only eye witness who saw the whole thing from beginning to end.
Charles