Severe internal hemorrhage? From what?
I would assume that is has no ill effects other than a little bit of stress. Not even so "mental" stress, more just natural instinct stress. Fish don't have the brain capacity to comprehend things such as mental stress.
Using flash is no different than a flash light, or even an overhead light... it's just for a small amount of time. Look when you turn on your tank lights with the ballasts, they flash 2-3 times first before completely staying on. So I guess every time that happens your fish starts to hemorrhage. What about when fish are in the wild? Many underwater cameras use flash. The bottoms of white boats can shoot off what will look like flashes....