On AC I took to my bed for two days the first round. Felt like I'd aged 60 years overnight. Could hardly eat because everything tasted off, even water. Tried a short walk to the shops and felt like I'd run a marathon. All the medics said get some exercise, you'll feel better - but I just physically couldn't.
On the three weekly cycle I got one good week, which is when I tried to get out and about, maintain social contact. I also tried to maintain a semblance of my gym routine but I have a tendency to go all gung-ho at the gym which was counterproductive so I settled for walking plus a few body weight excercises at home to keep things ticking over.
I concur with the drinking plenty of water - makes sense to wash the toxic substances through (and keep you regular!). But everything else, I think you have to play it by ear.