Bill Zebub
“It’s probably Matt Mercer’s fault.”
In my games, unless magically compelled, the players decide what their characters think, say, and do, full stop.
Yup. If the player wants to roll some dice because they can't decide quite what to do, fine, but I won't enforce any result of those dice. How they interpret it is up to them.
If they imagine their character being able to withstand the pain, that's their call. If they imagine their character folding like a wet newspaper, that's their call.