This happened to me this morning at 8:50 AM.
I am an incredibly heavy sleeper and I have one ear that has a slight hearing loss. Since I don't enjoy being disturbed while I'm sleeping, I sleep with my "deaf" ear up, so that random noises won't wake me until my incredibly loud alarm clock startles me awake.
This morning was no exception to that rule and I was sleeping with my deaf ear up. Somehow, I switched off my alarm clock while I was sleeping. I remember that I woke up at about 8:00 and realized that my alarm wasn't going off for the hour that I usually utilize my snooze alarm to get used to the idea of being awake. Half asleep, I pushed a few of the clock's buttons in a poor attempt to enable the alarm, then closed my eyes and fell back asleep. My last conscious thought was, "I hope I don't oversleep, that would really p*ss me off."
I usually drag myself out of bed at 8:45, giving myself 25 minutes before I have to leave for work. At 8:50, five minutes after my usual waking time, I heard a soft "knock knock" on the part of my bedroom wall that is closest to my head. I zoomed out of unconsciousness, upon hearing the knock, and said, "Come in!" I remember thinking that it was strange for my roommate to knock on the wall near my head if she wanted to tell me something before she left for work. When I heard nothing else and no one came into my room, I rationalized that my roommate had, for some reason, knocked on the wall to get me out of bed, something she had never done before. I looked at my clock, cursed when I saw the time, and leapt out of bed. When I opened my bedroom door (it opens into the living room), the silence in the apartment was deafening. My roommate was not in the apartment. The walls of our apartment are incredibly thin, so if she had knocked on my wall just before leaving for work, I would have heard the front door open and close and her footsteps as she descended our rickety stairs.
Realizing that no human could have knocked on my wall, the only thing for me to do was feel incredibly grateful that my guardian spirit cared enough about my being on time for work to wake me.