Given how many layers of clothing Tyson tends to wear - to provide a layer of protection, for himself mentally and for the dent in his torso - it’s not all that surprising that he tends to overheat in the summer.
Not that this fact actually encourages Tyson to remove layers. All this actually achieves is Tyson berating himself harder when a panic attack hits as he begins to hyperventilate. He knows its stupid, but when his mental state is so much worse in high temperatures, Tyson has to take the risk of having those extra layers.
His anxiety and OCD are relatively consistent the whole year around, but Tyson’s PTSD is always worst in hot weather. The most traumatic years of his life were spent running for his life across Afghanistan, Pakistan, & India. When he thinks of hot, he thinks of being afraid and helpless.
The heat brings those memories to the front of his mind much easier. Especially when it’s too hot to sleep, his restless mind thrashing for anything to hold onto. When a heat wave hits London, Tyson will go days without sleeping to avoid nightmares.