My thought is that it could it be related to general neuropathy due to activated viruses that were once dormant, where they are currently stationed, and the orgasm triggered the cascade described by nanna1, thus your histamines / mast cells are now on overdrive, attacking anything they find.
The Medical Medium theory on all autoimmune diseases (CFS, Febrio, Lyme, etc) are that dormant viruses in the Herpes family are responsible, latched onto nerve cells, and that the pain experienced is when your body's antibodies notice and rapidly fight the viral infection (inflaming and damaging nerves in the process).
Kind of a dumb question as most people are infected with no symptoms, but has anyone tested positive for Epstein Barr Virus (EBV) and / or any strains of the Herpes Simplex Virus (HSV1, HSV2, etc)?
These viruses in particular are noted for hiding dormant in nerve cells, particularly the brain stem.