In 2011 I got heat exhaustion. Since then I'v been sensitive to heat. Why did that 2011 heat exhaustion case make me sensitive for life? ?

I been sensitive to the heat ever since. I used to love the heat. Now it makes me feel weak, wonky, tired, sick and slow even in times that are considered minimal for some. I also have ADHD, Autism, Sensory Processing. As a kid I l loved the heat. But literally after the 2011 incident I have been heat intolerant. Had many of the symtoms in 2020 after hiking. In 2011 had headache, muscle pain dizziness, feeling faint, extreme fatigue. Not wanting to walk less than 100 feet to my kitchen.  Felt unwell for several days. Roomate/friend told me it's sun poisonig and encouraged water intake and salt. Gave me a fan. In 2020 felt naousous, dizzy faint. Felt like passing out. Was stupid and sat in sun again because I felt like falling and my friend told me get out of the sun. But I felt to dizzy to move Felt like passing out. Friend helped me get to AC and gave me water and put water on my neck like the Nicaraguans taught me. Since those heat exhaustion issues my heat tolerance has been low. I do not like anything above 80 degrees. I read sensitively can be more pronounced after a week. But never said for life. I am 35, petite, no MS, no drugs, no thyroid issues. Have ADHD Autism Sensory Processing. So why the sensitively that seemed to first  steam from my 2011 case? Thanks God bless. Be healthy.