Shadow Beyond Time (1970)

Based on H.P. Lovecraft's work, Shadow Beyond Time tells the story of Nathaniel Wingate Peaslee, an Arkham-born prodigy. At age 22, he becomes the youngest associate professor in the history of Miskatonic University. His bright future is disrupted when he falls into a coma, from which he won't seem to recover. That doesn't mean that his body doesn't wake up in the hospital, however, although that being is clearly not Nathaniel. 5 years later, Nathaniel returns to his body and from that moment on he begins an intense search to discover what happened to him. That's when disturbing visions begin to haunt him- visions that uncover things not only from his immediate past, but also from his own bloodline...