Some experiments:
Recently, as I was feeling better than is usually the case (no ejaculation since a while, zero sexual arousal, omega-3 doing their job to prevent my now-chronic symptoms like tachycardia), I tried some immune supplements anew.
I began with low-dose vitamin D3 (400 IU), which I took for a few days. I remembered that when I took it during the fall, one of the first apparent benefits had been that my dry mouth & throat, which felt almost irritated, came back to normal very quickly. I didn't know if it was a coincidence, so as I had the same symptom of dry mouth & throat last week, I thought it would be useful to try and see. The result of the experiment was the same : the dryness disappeared in 24h after beginning daily vitamin D3, and came back only a few days after having stopped to take it. This time, vitamin D3 didn't cause me strange symptoms of "pleasure intoxication". I guess that it's because I didn't have any moment of arousal and POIS state was kept in check, as I also had this "pleasure intoxication" triggered out of D3 by arousal. Last september D3 didn't have bad effects either, before I began to have some arousal episodes. However, this time I took less D3 (400 IU rather than 800) and only for a week, maybe it would have been different otherwise.
Whatever it be, I stopped D3 after a week and began zinc instead, since the beginning of the week. I had also already tried zinc last October, but only a few times because I felt that it aggravated my tachycardia and general POIS condition. However, as I had many problems at the time related to POIS, vitamin D3, etc., and as I was more frequently aroused, I wasn't really sure that zinc had such an effect. This time also, I tried it at lower dose, 15 mg daily rather than 30 mg. I take it during lunch. I didn't feel any particular effect in the first days but now they appeared. Yesterday I was feeling great in the morning (I could climb quickly the six floors of my apartment block without shortness of breath, which *never* happens during POIS and with tachycardia), but some time after the lunch I was suddenly tired, needed to lie down, and finally began to feel that several classic symptoms of POIS were here again. I checked my heart rate which was 92 bpm, clear tachycardia. Nonetheless I was not sure it was zinc because just after the lunch I had played at a video game for some time, which generated stress, and I never feel very good after stress. In the evening I took a warm shower and felt good anew, symptoms being gone. Heart rate 64 bpm, normal. Today I wake up in the same healthy state, but this time I was very careful not to do anything stressful during the day. Same thing happened however, a few time after my lunch and the zinc pill, I suddenly perceived that "POIS" was coming back, breath being shortened and less deep, feeling more tired. Heart rhythm 94 bpm.
So I guess that there may be two main explanations : 1/ immune activation due to zinc, as expected by nanna1 (the idea of taking zinc came from his posts, of course) ; 2/ zinc is linked to some neurotransmittors so maybe something happens at this level. I'm more inclined to favor the immune activation explanation, but I find a bit odd that a warm shower is sufficient to put an end to the symptoms, if this is so. Or the scheme is something like Zinc -> immune activation -> triggering of nervous symptoms -> nervous symptoms can be removed while immune reaction continues without manifest symptoms.
Also, I had my appointment in Pr. Amarenco's service, at Hospital Tenon (not with him personally). Nothing notable, the doctor was not very talkative. "There is seemingly a dysfunction of the autonomous nervous system" was all that she said about POIS. She wants me to come back for complementary examinations and mentioned a MRI (I said that I had had a cerebral MRI, but I read elsewhere that Amarenco & alii had studied the spinal column of previous patients). I'll have a notification for the appointment, probably not very soon, apparently. Ah, and she gave me cetirizine, to try.