I have episodes that I call 'crashes'. Are yours similar? I have leaden, overwhelming and incapacitating exhaustion (not fatigue) with arm & leg muscle pain (not aches), severe headache with sensitivity to light, sound and smell, no appetite, nausea, chills, inability to concentrate/listen/read/think/talk. I force myself to have 2-3 (8oz) glasses of water, take 2 Excedrin Migraine pills. I go to a bedroom with blackout shades and crawl under a pile of blankets, silence the phone, lay in the fetal position holding my head and pray I can fall asleep. This part lasts ~4 hours.
Then I can open my eyes to daylight and drink more water and move to the couch in silence.
Eventually I can tolerate the sound of tv turned way low but watching the screen hurts my eyes. I sleep on and off throughout the rest of the day/night
At some point I become hungry but nothing sounds good to eat, I wind up with either oatmeal or plain noodles because the smell of food makes me nauseas. Microwaved oatmeal is the fastest and safest for me to cook.
My last 'episode' I slept 26 out of 32 hours,
The next 2 days were like slogging through quicksand or swimming in oatmeal; no energy and a lot of time on the couch. After that I was so afraid of relapse into that state that I did very little the next couple days.
My longest episode was 10 days in a row and I had crashes ~every couple weeks.

Five months ago I started to keep a notebook/log every day. Laying open, on one page I write down what I am doing every hour of the day, the opposite page I write what symptoms I have that day. Looking at the log as I write during the day, I add up how many hours are spent on physical activity and how many with cognitive/thinking/brain work. Right now I am limited to 2 hours of each a day. After my last crash I was able to look back and see that I had way exceeded my cognitive limit-the week prior I had 3 days of 4hrs cognitive work and 2 days of 3hr work. I could also see that the day before the severe crash, I had been really tired early in the afternoon-that was the start of the episode.
Every single 'crash' episode is the same thing: I feel good and inadvertently stretch my limits, then do it again and again until my body says 'heck no-I am shutting you down!'.

The episodes are farther apart and last less days the more I pay attention to my limits. it's been over a year since I had COVID, a positive test but did not require hospitalization. The symptoms haven't changed or improved, I have learned (through PT/OT/Speech Therapy) to change my activity to improve the frequency and severity. It just plain sucks that my life went from marathon runner, ER nurse, traveler to 2hr light physical and 2hr brain work a day. Mentally I haven't accepted and keep forgetting my limitations, ergo the repeated crash episodes.