Because cold temperatures affect the brain. Cold compresses matter, including gray matter. The brain becomes smaller for a while, which causes painful sensations. It is believed that if you practice drinking in this way very often, then the chance of meeting old age with dementia rises to 30 percent. Therefore, you only need to drink warm water.
This occurs when something cold touches the nerves near the palate, which causes the blood vessels in the front of the brain to constrict, which causes pain.