Despite the umbrella term that is used for it, Long COVID is “not really one disease,” says Krumholz. Internal tremors may be indicating one of the subtypes of this condition, with implications for treatment. Krumholz hopes that identifying the various symptoms of Long COVID will help researchers identify causes and pinpoint a broad range of therapies for patients for whom effects of the virus continue to linger and whose lives have been severely affected as a result. LINK
That's one of the things my ME started with. That and much more and they were sometimes very visible, feel like shivering from a fever, but mostly at a lower "buzzing" level and remained for years. Very commonly reported from the start in LC. Can be found all over the place on the LC forums. And I'm pretty sure reported in the first patient-led papers. But of course it's almost always reflexively dismissed as anxiety. Stuff like this is why MDs believe that anxiety is super common and disabling. How freaking ridiculous that when they make mistakes it actually reinforces their beliefs as being correct.
Internal tremors happen with hypothyroidism. I suspect it may happen in people with hyperthyroidism too. Thyroid diseases can screw up one's cortisol output, and it can end up being too high or too low. Both of these situations can lead to internal tremors.
we have at least 1 thread on it Members only - Strange Sensations/"Bad Vibrations" | Science for ME (s4me.info)