I'm not sure I belong here as I wasn't settled on hrt very long at all before it turned on me.
Timeline:
Aside from early onset, my timeline followed the STRAW perfectly.
Ages 36-38 menstrual changes, night sweats during periods.
Age 38, periods mostly stopped. Anxiety, palpitations, trembly legs, severe flushes, fear, breasts size decreased a little.
Age 39, started hrt. First 6 months: Major emotional swings. Palpitations, flushing and trembles cured, breast size back to previous. Next 5 months: life is good. End of 39: Major depression and unwell feeling. Age 40: stopped hrt. Immediate relief, still improving and gets better every day. I am having return of some physical symptoms, either they are less severe now, or after all I've been through I'm better equipped to cope with them.
I find your histamine connection interesting, as I remember describing my feelings as almost like an allergic reaction, but I had no real allergy symptoms like sinus, itchy eyes, breathing problems or rash.