What causes chills and fever that go away in a day in 80 year old?

Between 40% and 61% of patients who experience stroke develop fever, and those patients with fever are far more likely to die within the first 10 days after a stroke than those with lower temperatures. See the MD or get to the ER when you see 103F (39C)

A temperature that high is life threatening to an elderly person. I would suggest you contact your father's primary physician.

Really, I would not fool around with a fever that climbs to103. I would get a same day appointment with the doc and if that is not possible, go to the ER.

I would check for a UTI. This is very serious in men. Chills are a sign.

This happened to my mom a lot in the last year of her life while in a nursing home for advanced stages of vascular dementia. After all possible causes had been ruled out the doctor told me that her body was losing its ability to regulate its temperature.

Diverticulitis, Ulcerative Colitis? Some things that are "chronic systemic" can wax and wain and temp right along with it, although usually more of a "low grade" temp, like less than 100.5. A Dr. visit and blood draw are definitely in order, something that hasn't been discovered yet could be escalating. Best to head it off before they wind up in big trouble. Good luck!

Fever generally means infection somewhere in the body.

I can only think some medication is causing the return to "normal" briefly. You don't say how long this has occurred, but tell his doctor. Chills and fever (if only briefly) indicate some sort of infection. He may have a UTI or HPV II virus or shingles virus which lays dormant inside those who have had chickenpox (or being exposed to ones with chickenpox). "Spikes" in temperature are usually normal, but NOT 100 - 103. Get him in and check for an elevated WBC count.

I don't know what is causing it, but I think you should schedule an appointment with the primary physician and ask them to do a full blood screening just to be on the safe side.

Maybe it is an allergic reaction to some meds or something he/she is eating or the combination of the two. If this is happening on a regular basis, keep a pill and food diary to see if there is a common denominator. And let that person's primary doctor know what is happening.