Since retiring a few months ago my physical health has held up admirably well other than some nagging recurrent lumbar pain. That got interrupted abruptly a couple of days ago when out of the blue, while researching something at our public library, shaking chills emerged. I had no symptoms to localize an infectious source. There was accompanying generalized achiness and a severe tremor that kept me from using my keyboard or cell phone when I got home. The purpose of this physiologic response is usually to warm the core temperature, which happened about an hour later, peaking at 101.1F, pretty much as my textbook of the 1974 Harrison's Internal Medicine with the bright blue cover described it. Once suitably febrile, the shaking stopped. In an hour or two the fever had resolved though I felt exhausted and just a shade achy suggesting this might be a viremia rather than a bacteremia. The temperature elevation never returned and having cancelled my appointments for the following day, I just stayed mostly horizontal, allowing my return to mostly baseline the day following. I do not know what caused it. Being an experienced physician, I recognized what it was, had seen it many times before and never felt sick enough to either call my doctor or head off to urgent care. Back in action today.