I have the same problem but it's usually the result of getting several pains at once and in the middle of the night. I get terrible intestinal pain and this usually accompanies the rare times I've fainted. The cause isn't apparent but could sometimes be related to the suppression of peristalsis caused by the medications. It's always been a couple bad pains at once but one seems to reinforce another. I try to assume positions where I won't be injured if I pass out.

Avoiding gassy foods after noon helps for me.