I haven’t read through all of the responses, but if I’m not in a full crash (i.e. just needing to sleep, stay completely immobile, and rest as long as my body needs), I will do some of these other gentle activities. They’re all ones that are recommended by my doctor, who has been a great support.
1. Eye exercises for vagal nerve stimulation - “Accessing The Healing Power of the Vagus Nerve” by Stanley Rosenberg is a good resource.
2. Manual lymph drainage - there are YouTube videos on how to do this
3. Sit outside in the sun (or in front of a sun lamp) for at least 10 minutes/day - great for Vitamin D
4. Forest bathing - fancy words for spending time around trees, especially evergreens. Not only does it feel nice and relaxing, but the trees actually give off antimicrobial compounds that help the immune system. You don’t have to do a full on hike to get the benefits. Just sit on a stump or at a picnic table, for example. Here’s one of many books about it: “ The Secret Therapy of Trees: Harness the Healing Energy of Forest Bathing and Natural Landscapes” by Marco Mencagli
5. Cold showers in the morning, warm showers in the evening.
6. Have protein shakes, green powders, electrolyte drinks, fruit, and water on hand for the days you just can’t cook for yourself.
7. Hum and sing along to your favorite music (another way to activate your Vagus nerve).

I don’t find that any one of these is a cure-all, but they each have their own benefits, and I do feel better if I can do them fairly regularly.