I've had a histamine reaction to pork, but not all pork. I wonder if it depends on what the pigs were fed. I mainly avoid it.

Overload can indeed occur when you are exposed to multiple allergens. I can handle a mild allergy to cats if I avoid outside allergens, diesel fumes and foods I am intolerant of. For me Quercetin/Bromelain works for a low level of histamines so I always try that first, then half a Claritin, then Benadryl if the lower-level remedies aren't working. It can actually help to take Quercetin/Bromelain daily during allergy season and half an hour or so before heading out to do yard work.