I've always enjoyed drinking hot coffee / tea on hot days, and found out this is a sort of tradition for some people (e.g. kopi in Singapore). Supposedly, it cools you down by kickstarting your sweat, but for me it also makes me feel instantly clearheaded (whereas the caffeine high takes 30ish minutes).

Maybe some of us need that kind of stimulation just to feel fully awake. I'm a generally lethargic person, and in that state I can't really think clearly. A little shock to the central (or sympathetic?) nervous system helps counteract that and get the ideas or work flowing.

I’m convinced that it’s the hot water on the back of my neck opening up blood vessels and increasing oxygen to my brain.

This sounds like it's more related to heart attacks. I don't think this is healthy.

Have you tried a sauna?

I’m going to try this