By no means is this page an exhaustive list of the risks you encounter when you masturbate outside the norm.
As stated earlier, your best bet is to always use common sense and imagine the worst possible thing that could happen if something went wrong. For instance, if you think it would be cool to masturbate with a large mirror hung several feet over your bed, what would happen to you if it fell on you? Ordinarily you'd probably be smart enough not to hang a mirror over yourself, but in the heat of a masturbation session, sometimes we do foolish things. And sometimes we get hurt.
Don't hurt yourself masturbating. Stay safe when you enjoy yourself – that way you can still enjoy yourself tomorrow.