This article has a theory straight from investigators.
“Now, investigators have pieced together a theory of how Saget died.
Authorities checked the marble end tables and counters in the bathroom, but found no traces of blood or hair. Now, they believe that Saget lost consciousness in the bathroom and fell backward onto the marble floor, striking his head.
Police believe that a groggy Saget regained consciousness and stumbled into bed, where he again lost consciousness and died. His time of death was estimated to be around 4:00 am, approximately 12 hours before his body was found.”
What Really Happened to Bob Saget? New Details on His Final Hours