As far as I can tell, any time you can line up your shot, you can shoot. While you're hanging from a wall by your fingertips, probably not, and they've said that when you're knocked down you have to choose between getting up or shooting. Other than that, you're free to pull the trigger anytime.
I hear shooting while getting up is still possible, but at a huge accuracy penalty, using only one hand and getting up from your bum and all.