I was reviewing a note today, written by a nurse practitioner I work with, on a 60 year old male.
Under hobbies it stated sleeping.
Most define a hobby as an activity that is regularly undertaken for pleasure, typically during one's leisure time. A hobby is whatever you do in your free time. A person who engages in an activity solely for fun is called a hobbyist.
So, depending on how you emphasize the definition sleep could be considered a hobby: undertaken for pleasure and during one's leisure time.
I guess the sticky point is whether or not sleep represents an activity.
I'm pretty sure I would have considered sleep a hobby in college...I'm just not quite sure about the rest of my adult life.