And then you start to make the lists. There are, perhaps, a hundred things that could have gone wrong. You sort through them, on the two-mile drive--the best case, the worst case.
Best case: He fell asleep in his chair. He'd been complaining about waking in the wee hours and not being able to return to sleep, then being tired all day: Perhaps he sat down in front of the TV and dozed off, then didn't hear the phone(s) because the TV was too loud. Maybe you'll come in the back door and he'll awake with a start and you'll both have a laugh.
Worst case: He fell down the basement stairs and broke a leg, a hip...a neck. Or he had a stroke and has been unable to get to the phone. The thought of him having lain there injured or incapacitated for hours or longer is intolerable. Noon-hour traffic is heavy and slow.