This might be a little random atm, but im looking at factors that could increase body temp or even induce fever. This example would also be immune related or regulated.
Cold intolerance seems to be a symptom in many with PFS.
Interleukin 6 (IL-6) - I can change your body’s temperature set point!
Interleukin-6 is important for regulation of core body temperature during long-term cold exposure in mice
Interleukin-6 (IL6) is a cytokine important for inducing the fever response during infection and has been reported to uphold core body temperature during acute cold exposure. Recently it has also been indicated that IL6 in serum increases in cold-exposed mice.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6158403/#:~:text=Interleukin-6%20(IL6)%20is,increases%20in%20cold-exposed%20mice.