My experience with antihistamins
I am going to talk really briefly here. I am a doctor and have suffered from pois for a very long time, from what I understand the most accepted hypothesis is the allergy hypothesis so I tried antihistamins and got great results so I am going to give you all some tips based on my experience.
Pois is theorised to be type 1 Hypersensitivity, in type 1 hypersensitivity the inflamation cascade begains immeditly after allergen encounter, then you have local mast cell histamin degranulation and systemic bsophilic histamin degranulation. The histamin doesn't cross the blood brain barrier, instead the inflamation and sickness like feeling is due to the inflamation cascade and not directly due to brain histaminic recptors, so taking gen 1 antihistamins doesn't make symptoms like brain fog any better, the histamin regulate arousal in the brain actually. But there is a catch, because first gen antihistamins are lipophilic they enter tissues and work much faster so they can be used when you are in a hurry.
Also for the antihistamins to work you need to take them a while before so they cover the histamin receptors and prevent the inflamation cascade from begaining. Second gen drugs take 1 hour minimally, first gens take 15-30mins but they can cause sedation so take them only at night.
From my experience I got the most results when I took two tablets, one and half hours before orgasm. That eliminated all of my physical symptoms, reduced my brain fog a lot. Now I only feel really sleep the next day nothing more and huge amount of caffein help with that. You can also take paracetamol and nsaids that cross the blood brain barrier such as ibuprofen, ketoprofen and naproxen (this one stays in your system for long time so it can be useful) to lower the inflamation but they didn't do much for me.