Why am I so Sensitive to Hot Weather?

[RT93]

25, Male, 6'2, 280.
Back in 2010 Early summer I attend a very hot Chicago Blackhawks Parade. I didn't eat much nor did I wear a hat that day, my mistake. I was waiting for it to start which got delayed. Felt hot, sweating like normal when its hot out. Then I started feeling off. Light headed, light in my eyes was fading, next thing I know I'm out like a light. Total blackout. A lady next to me woke me up on the ground. Gave me water. I went into nearby store ate something and drank a big thing of water.
Later that day I felt much better, didn't go to the hospital since I felt fine.

Now, ever since then when its hot and sunny out even with a hat on and drinking water I feel so sensitive to heat. Hard to enjoy summer. Not sure If I suffered a heat stroke that day or any brain damage. But i will say i have felt slightly different ever since that.
Especially, first week of school I had that time a huge panic attack which cause me anxiety which is a big story for another time.

Recently this year I had a MRI on my brain for testing something. It came back negative and dr said I have a nice healthy brain.

So what I'm wondering is why am  I, 8 years later so sensitive still to heat?
Did I suffer a heat stroke?
How do I tell if it caused any
Brain damage?

Thanks to whoever reads this and takes time to answer.