Looking for a science fiction short story I believe is titled “Seven Century Summer” or something like that. From what I remember a modern man had an accident and traveled forward in time, to a post apocalyptic world. There his consciousness inhabited the mind of a native. There was a great being in a tank of some sort.
I literally read this yesterday and thought that it fits.
Midsummer Century (1972) (A book in the Haertel Scholium series) A novel by James Blish
In the year 25,000 A.D . . . When John Martels returned to consciousness he found himself the Delphic Oracle of a world far different from the Twentieth Century. Humanity had risen and fallen three times and was back once again in a semi-primitive state. He shared his oracular powers with a mind and a device left over from the last Rebirth . . . but the real problem was not rebuilding civilization, it was that another genus of creatures had arisen to claim inheritance of the world--the evolved, strangely intelligent birds, whose priority was the elimination of the world's former masters.
This book actually contains one novella-length story, “Midsummer Century,” and two short stories: “Skysign” and “A Style in Treason".
As pointed out by user14111 the short story is available on the internet archive.