In short, I believe MS and POIS to both be immune disregulation disorders and like Austism spectrum disorder (sorry last name i've heard of) are likely if not the "same disorder" they are 'cousin' disorders which have similar or the same treatments ultimately.
My Wife has Multiple Sclerosis (clinical Diag 2007), and experiences most of the symptoms of POIS after orgasm, with symptoms going away, some suddenly, others gradually, for 3-7 days after orgasm.
She has had these POIS symptoms since at least 1997, her MS was diagnosed in 2007, but at least 1 neurologist has told us, the initial onset of the Multiple Sclerosis could have been as early as the early 1990s when my wife recalls having unexplained numbness, weakness, and tingling in her fingers, with associated fogginess of thought, and a general feeling of malaise unassociated with any other physical or mental conditions (e.g. not associated with her period, with an injury, etc.)
This is of course just my wife's story, and if POIS is like most diseases, it is better classified as "a grouping of symptoms that seem to have a common source/cause(s)" much like Autism has gone through a varied change in it's definition and classification. As such, it would align with Multiple Sclerosis, which is itself, more of a spectrum disorder than a cut-and-dry disorder. Multiple sclerosis is widely believed to be caused by one or more immune disfunctions where in the myelin shealth protecting nerve cells is attacked by the immune system resulting in damage up to complete destruction of the shealthing. Much like electrical cords in our houses and devices, the nervous systems does not function well when its "wires" are uninsulated and thus can short circuit in any number of ways.
In my wife's case, there is the "baseline" disfunction she seems to have from her Multiple Sclerosis (MS) which includes issues with cognition and motor function as well as overall physical and mental fatigue and weakness in specific muscle groups. While there is some variation in the severity of the various MS related symptoms from hour to hour and day to day, they fluctuate little outside of her going through a stressful event such as having her period, having to be outside in hot weather, exercising more than normal, etc. resulting in a fairly predictible set of limitations we can plan our lives around.
Then there are the group of symptoms she has starting about 1 minute after an orgasm and which stay last at a level of "this is effecting my everyday life" for 3-7 days. These symptoms include worsening of what appears to be some of the same symptoms she suffers with daily as part of what has been attributed as "MS symptoms" (e.g. fatigue, motor control issues, specific muscle weakness, brain fog, cognitive issues, etc.) as well as some which could be MS symptoms, but which are only experienced during these 3-7 days post orgasm, and a third set which are symptoms which we strongly believe have zero connection to MS as they are as strong now as they were 10 years PRIOR to the MS diagnosis.
One theory is that my wife suffers from some combination of disorders related to autoimmunity. If a person's immune system is disregulated, misformed, or in some way not functioning as we understand to be "normally." Abnormal immune systems can be unpredictable to even the most experienced medical professionals, let alone the average person. Now if you add in the fact the medical profession is coming out more and more frequently with "corrective" statements regarding disorders and diseases (e.g. Autism's progress from single disorder to spectrum, etc.), it is no wonder we have so much confusion about which disease causes which symptoms and what disorder I do or do not have all so I can try to treat myself in a manner that improves my life to a better place past the current suffering/limitations/etc. I am experiencing now.
As such, I can't see why the two can't be connected, and in fact, may simply be different expressions of the same illness at the root, just expressing themselves via different mechanisms. It could also be that there is a synergistic relationship between the two.
With my wife, she has in the past, experienced fatigue after orgasm. Then again, she also experiences fatigue after what most people would call a 'very short walk around the block' level of exercise, which may at worse, raise a slight sweat on even a very out of shape person. Could it be that her immune system is simply "out of sorts" due to past traumas on that system from various life experiences (really bad night on the town, having surgery, etc.) and that basically a Hard Reset is required. Until then, the immune system may be so disregulated and outside of normal function that not only does it view everyday stresses onthe body and the subsequent chemical releases inside the body (e.g. Cortisol, adrenaline, hormones, etc.) are viewed as something "bad" which this disregulated immune system sees as a threat to which it must respond. Then in its disregulated response, the disregulated immune system attacks parts of the body instead of "real" intruders like bacteria or virus. If this is the case, then couldn't it be that, as some have suggested, one of the triggers for this disregulated response is one or more chemicals introduced into the body at or around the time of orgasm (hormones, GABA, etc.).
I am certainly no expert on POIS, but I would say with 99% certainty, my wife suffers from it as well as suffering from clinically diagnosed MS (lesions visible on MRI's, etc.)
