Sounds like autonomic dysfunction with your heat intolerance symptoms. I read an article of a girl who was first diagnosed with "psychogenic seizures" likely due to stress but finally was diagnosed with Postural orthostatic tachycardia syndrome (POTS).
There are plenty if articles on dysautonomia if you want to research further.
"Dysautonomia or autonomic dysfunction is a condition in which the autonomic nervous system (ANS) does not work properly. This may affect the functioning of the heart, bladder, intestines, sweat glands, pupils, and blood vessels. Dysautonomia has many causes, not all of which may be classified as neuropathic. A number of diseases can feature dysautonomia, such as Parkinson's disease, HIV/AIDS, multiple system atrophy, autonomic failure, postural orthostatic tachycardia syndrome, and autonomic neuropathy." - Wikipedia.
Have you been checked for FND a nurologist is the person u need to see ,