For Wiccan ritual, how can the chronically ill raise energy?

I keep reading in various books that one shouldn't perform or take part in ritual in general, and magick in particular when one is not feeling well. This poses a quandary for for those with chronic illness. I deal with Chronic Fatigue Syndrome/Fibromyalgia, and ALWAYS feel exhausted and unwell. Are there ways to compensate for cases like this, to make ritual more effective despite low physical energy?