Yes and the other researcher remarked: "It seems likely that POIS represents a spectrum of syndromes of differing etiologies".
If you concentrate on individual "casuistics" sourced from NSF discussions, yourbrainonporn, Dr. Lin's pages, answers portal like Yahoo, reuniting, drug-related forums, etc., you will see, how many people suffer from very similar, yet different (in a subtle way) problems following orgasm/sexual activities.
I wouldn't exclude any thinkable cause, starting from purely psychosomatic origin (if there exist phenomenons like loss of the ability to walk, speak, urinate etc., why not post orgasmic disturbances?), side effects of drugs, underlying illnesses capable of mimicking other conditions (like Lyme), autonomic dysfunctions, bacteria, to discussed autoimmune or hormonal ones. Also, I wouldn't condemn the placebo effect in cases of so called "successful treatments", moreover in situation, there are no visible/noticeable organic changes or abnormalities in the body, "just" some hormonal imbalances or allergy to own semen.