I looked a bit into this as a treatment option for my chronic infection (in addition to abx). It's used as a complex protocol in some german alternative hospitals for treatment of cancer.
Your immunesystem gets massively activated, it's not just an increase of temperature like you have in the case of passive hyperthermia. Given that hardly anyone knows the immunological background of his CFS, I find it highly experimental and dangerous. Anyway, this treatment seems to be a big burden even for cancer patients, who normally have much more energy compared to a CFS patient. I find it an interesting treatment option, but until know it seems to dangerous for me to try it, although I found a doctor who would try it with me.
In Germany they use picibanil (probably comparable to pyrogenal ?) and some vaccines together (which potentiates the effect), given intravenously over 30 minutes. Then the fever comes and stays for 8-12 hours. This procedure is normally done 3 times a week. If you are interested I could look for the research paper which describes the procedure for cancer treatment. They are explaining the protocol in detail in it.