For me, POIS was definitely thyroid related (I'm willing to bet this is the case for many of you). I never had POIS, until I was diagnosed with a thyroid condition. After suffering for years with the condition, and reading many books, I pieced all the pieces of the puzzle together and FINALLY started to feel normal. Now, POIS isn't anywhere near as severe as it used to be. Everyone here, get your thyroid checked. Get the full thyroid panel tested which is: TSH,FT3, FT4, total t3, total t4, reverse t3, and antibodies. Most doctors won't check reverse T3 and antibodies on their own, which is VERY important to check, so ask for it. If the test reveals a thyroid disease, and the doctor is willing to prescribe T4 only (like most doctors), FIND A DIFFERENT DOCTOR. Chances are you will never feel normal on T4 only (some do, but many people are suffering on it). Before starting the meds, get a full iron panel to check iron levels. A cortisol test should also be done, saliva testing is the most accurate (this is usually a private test that can be ordered online and sent to a lab). This is very important as the thyroid meds will not work without optimal iron and cortisol levels. If needed, start an iron supplement and hydrocortisone (cortef) for some time before you begin thyroid treatment.
Now for the thyroid treatment itself. I would start off with a nature dessicated thyroid which contains all the thyroid hormones, T4,t3,t2,t1. This is much better than the miserable t4 only meds (which is an inactive hormone that needs to be converted to the active hormone, T3). The brand Armour (USA version) changed their formula years ago, and people are reporting it's not as effective, so you could try ERFA, which is made in Canada. If your iron and cortisol levels are optimal and the dessicated thyroid is not working, you're just like me, but there's still hope. Some people don't convert T4 into T3 very well, instead it pools around the cell (labs look good, meanwhile it's not getting into the cell). If this is the case, the only way to clear the reverse T3, is to take T3 only. So many people suffering could benefit from this under-prescribed thyroid treatment. However, by taking T3 only, your labs will look much different, so it's important to dose yourself based on symptoms. And trust me, you will know if you are over/under medicated, the symptoms are classic.
Since most thyroid disease is an autoimmune condition (antibodies are present), it's also important to eliminate gluten from the diet as this adds gas to the fire.
It seems like most doctors specialize in everything but thyroid conditions. So if you are having a hard time getting dessicated thyroid, t3, or hydrocortisone prescribed, PM me and I'll let you know where you can get it
this seriously saved me. My libido is now through the roof and POIS only lasts a few hours. Some times a day, but hey, I'll take that over 10-14 days like it used to be.