The two best things to trigger sleepiness (and they could possibly be combined for effectiveness ):
* sex
* hot bath or shower

My husband votes "yes!" on the first one and "yeah, sure, whatever" on the second.

It's true...sex causes the brain to release oxytocin, which results in the production of sedative endorphins – natural analogues of morphine.

And the hot bath raises body temperature (and of course is relaxing in itself)...yet it's the subsequent drop in core temperature that triggers sleepiness.