Bob Saget, the comedian and actor, died after what appeared to be a significant blow to the head, one that fractured his skull in several places and caused bleeding across both sides of his brain, according to an autopsy report released on Friday. The findings complicated the picture of Mr. Saget’s death that has emerged in recent days: Far from a head bump that might have been shrugged off, the autopsy described an unmistakably serious set of injuries that would at the very least have probably left someone confused, brain experts said. The report, prepared by Dr. Joshua Stephany, the chief medical examiner of Orange and Osceola counties in Florida, ascribed Mr. Saget’s injuries to a fall. “It is most probable that the decedent suffered an unwitnessed fall backwards and struck the posterior aspect of his head,” Dr. Stephany wrote, referring to the back of the skull.