@awnlee jawking(this is from memory, I'm not about to re-re-reread it again at this point)
18-year old goes into a coma, awakens as a John Doe in a hospital 45 years later without having aged. He subsequently discovers that the original "him" died all those years previously.
His sister is the only family member still alive, at least one school friend is also still alive.
That's all I'm going to write on the plot, not about to give the rest away for those unfortunates who have not read the story.
I'd classify it as time-travel. If that is a sub-genre of SF then it could maybe qualify, except that there is no attempt made to say how all this came about.
Oh, and his "Repeat Performance" has a somewhat similar plot.
Now, "Radio Days" - also by coaster2 - could maybe be classified as SF.