Passing out at certain dangers could be tonic immobility. Like people pass out when they see a lion, bear or something. Ofc, it doesn't happen to all humans and passing out isn't really related to that, but it might work.

On the fact that humans have the conscious thought to debate whether this is possible means that it is right? It's quite easy to up and limp to the ground as if you had died. So I guess I have to say yes I think so.

so i made some research about Tonic Immobility for human and it said that humans can do it if they are sexually assaulted so they can defence themselves from it. what do you think about that? i know its not the only way to make tonic immobility and that there is another things to do tonic mobility in it .

I wasn't really giving this thought till you brought up the blanket analogy. Interesting point, but that could just be the fear in us. If a building is about to collapse on you, you put your hands above your head and close your eyes right before it hits you. I don't know if that's a good comparison. But if you want to be really literal about it, if playing dead was in our nature we would play dead, which I don't think we instinctively do.

Of course if it is actually present, it won't be applied in every case but I have to agree with some of what you said.
If the flight or fight instinct was in place as a defensive mechanism, why would you need to play dead. Unless you knew that a bear wouldn't attack if you play dead, you would fight it or run from it. I don't think it would be an instinct but rather a conscious decision.

Evolutioin isn't governed by pure efficiency. We have left over organs which we can't even use and which can cause serious medical problems. Our instinctive reaction to stressful situations is to focus on and replay the memories of them in our head (which was useful back when stressful situation were usually also life threatening and thinking about them made it more likely that we would prevent them from happening to us again) making us prone to unhealthy anxiety based issues which can lead to suicidal tendencies. We can get addicted to the adrenaline from our fight and flight mechanism leading some of us to take part in needlessly dangerous activities for adrenaline's sake and some of us to even literally inflict wounds on ourselves.

What I am trying to demonstrate is that proving that we do not need tonic immobility is not proving that we do not still have it. It would just be another useless remnant of so many common ancestors.