Mine is... mowing the lawn! I know, I am kind of old-school with this respect. But I really enjoy this, being outside, getting my weekly dose of D-vitamins, etc. In addition, this is a quite useful activity for the house.
I was in fac about to consider biking a bit during the week-end, but the temperature is planned to reach 40 Celsius... France is hit by a heat wave at the moment, and I therefore probably won't bike...
Do you eat enough? If you're not counting calories, you could easily, accidentally, start eating less for whatever reason, and that alone might cause fatigue. Add exercise, and now you need even more calories! (depending on whether your weight was okay to begin with).
I had a lost of appetite during the week I was COVID-positive. I guess my current state is originating from many sources: COVID recovery, heat wave, being a bit weaker than usual, etc. I guess I will slowly and slowly get back on tracks.
Cheers and thanks for asking! :-)