Why does hot cocoa make me tired?

Caffeine is supposed to give one a jolt of energy, correct? So then why does this delicious hot cocoa always make me sleepy?

A completely unrelated question: What are corn syrup solids? I saw that ingredient on a food I was eating earlier and it sparked my interest.

I don’t think hot cocoa has much caffeine in it. Of course, caffeine content is the one thing that they do not have to put on the label (Why not?) so I don’t know how much it has, but I’m sure it’s much less than coffee or tea. What cocoa does contain is warm milk, which is a famous folk remedy to help people fall asleep.

It’s more the warmth than anything else. Even warm milk, it’s more the warmth than the milk.
Any low/no caffeine warm drink will probably have the same effect.

–I think Tryptophan figures in here if I’m not mistaken. In any case, the larger question is, why do I get heartburn from the hot chocolate that comes out of those little envelopes?

Cocoa powder contains theobromine, a relative of caffeine and also a stimulant. Theobromine - Wikipedia