Read more here:
Why, when the temperature rises, it gets cold: is the body hotter?
The fact is that it is important not only what temperature, but that the temperature is rising. And partly the mechanism of temperature increase leads to unpleasant sensations.
Yes, the fact is that all metabolic processes in our body are controlled by enzymes. And enzymes can work under very harsh conditions. The ideal temperature for them is 36.5-36.9. If it is higher, then the activity of enzymes decreases, and if I am not mistaken, at about 40 degrees they stop working altogether. This is called thermolability.
The basis of metabolism in the human body is played by enzymes that catalyze thousands and thousands of ongoing biochemical reactions. This is the foundation of life. It often happens that the proper activity of enzymes is manifested in a very narrow temperature range. (Although, it's not just temperature that matters. The pH range at which the body can function is also very narrow.)