Blows to the back of the head are far more dangerous than getting hit from the front. A fall backwards, hitting his head on say the hard tile floor of the bathroom, might have been enough to do it. He could have crawled into bed, fallen asleep and into a coma, and died from intracranial bleed.
Reminds me of the old joke of the guy on trial for stabbing another guy to death: “well you see your honor I was just sitting there holding my knife and this guy comes running around the corner right into it....... twelve times”
My thoughts too. He slipped and smacked his head very, hard on something in the bathroom and either walked, or crawled, into bed thinking MAN that hurts! It is sad no matter how it happened.