This is "excited delirium" for those interested:

https://en.m.wikipedia.org/wiki/Excited_delirium

This is absolutely a relevant concern. And even without factoring in drugs or delirium, just because a person is lying quietly one moment doesn't mean they couldn't instantly freak out once restraint pressure is released.

You see this happen all the time with restrained animals. If you hold them down completely, they stop struggling, but the moment they feel a opening, all hell breaks loose.