If you’ve ever wondered why …
I experienced this for the first time ever while sitting at the beach watching yet another incredible tropical sunset, sucking a passion fruit granita, locally called ice sludge. Suddenly my head felt as if held in a vice, terrible pain engulfed me and the mind offered mad thoughts such as having a stroke – not helpful. I held my temples with both hands hoping this would pass – and miraculously it did.
The medical term for this experience is sphenopalatine ganglioneuralgia, also called brain freeze, and if you never had one before, don’t even think about trying to have that experience! Meaning, do not drink anything that looks like a glacier in a glass.
Here is an explanation by the folks at SciShow about what happens inside your head at such time: