I notice that when I don't sleep well the night before, or an unplanned activity takes precedence over conserving energy, I stay cold that day or the following day, and it can take hours for me to warm up. Even if I get under the covers with wool blankets and a heated mattress bad, it will still take hours to warm up again. I just wonder if fatigue (PEM) is interfering with the body's ability to maintain homeostasis, i.e. adequate body temperature. My thyroid levels are fine, but I'm not a good converter of T4 to T3. With my current test results, I doubt if any doctor would recommend thyroid meds, but I might ask at the next visit. I know there's a LONG list of symptoms that occur when someone gets PEM. I would appreciate it if people could just focus on the issue of being cold, and not all the other countless symptoms, because I've probably had them at one time or other too. So who else freezes when they've overdone it or didn't sleep well the night before? Theoretical hypotheses and background regarding why this happens are welcome, if anyone would like to tackle that aspect. Thanks.