Actually when we go to bed we’re kind of deciding to go to sleep. Some people take 5 mins, others close to an hour (me) but its a decision. Your thoughts, ego, are also not the same as the body. Maybe its some kind of negotiation. The body reads some signs then maybe tries to guess if its time to sleep. Other times its the other way around, the body dexidoes to do it regardless of what your mind wants.