Physical Danger
Hospitals are very sterile environments...or at least, they're supposed to be. No system is perfect, and you'll be getting up close and personal with a lot of patients. Lots of hand-washing and regular changes of clothing will become part of your daily routine. And, of course, you'll be a little bit closer to the cold and flu when 'tis the season.
Other dangers include being severely grossed out (like, where's-the-nearest-vomit-receptacle-level grossed out) by what you see, physical complications from being on your feet all day, and working odd hours with very little rest. Those things can hurt you over the long term, and so can calling a candy bar and an energy drink "dinner" four nights a week. Try to eat an apple now and then. We hear that one a day keeps the doctor away...unless you work in a hospital.