Did he get too much morphine?

I'm a new nurse and am still learning drug doses and such.
My brother had a lapchole today. After the surgery he was in his room resting comfortably. A student nurse comes in and asks if he's in any pain (syringe of pain medication in hand), he said a little only when he tries to urinate. She asks if he wants the pain med and he says sure. So in it goes.
A little later he's feeling light-headed and really sleepy. Student nurse comes in and I asked how much morphine she gave him...she gave 8mg. Isn't that a bit much for a pt who really isn't in much pain??? I would think that 2mg would have been much more appropriate. I'm assuming the doc wrote a range for the pain medication, like 2-8mg prn.
What do you all think???