Asklemmy

Warm. Tummy full. Sleep now.

Well, it was most likely the indirect drop in core temperature, or a change in your nervous system's detection of temperature difference.

When you warm up the skin, all the little capillaries open up at the surface. It isn't only at the source of the heat. So your body now radiates its heat through the skin, dropping core temp slightly.

A decrease in core temp is known to be part of the normal sleep cycle. This is one of the reasons a hot shower can contribute to faster, better sleep when taken an hour or so ahead of the intended bedtime.

However, another part of the sleep cycle, or rather how our bodies work leading up to sleep, is that when external temperatures feel cooler, the adaptations our bodies make promote sleep, and improve sleep. It's why a common bit of advice is to keep the sleeping area cool. But, if you trick your body into feeling a different gap in external and internal temperature, it often serves the same purpose. Our skin isn't that great at determining direct temperature, as in "the air is 70 degrees". What it is good at it "the air feels 30 degrees warmer than me". So it can be fooled sometimes.

Add in the comfort of cuddling, with the full stomach pulling blood towards the stomach, and you've got a nap bomb.

There's been some good research into this, and if you look up thermoregulation and sleep, skin warming and sleep, as well as general information about the sleep cycle, you'll run into at least articles reporting the studies. Most of the studies are paywalled, but if you're sufficiently motivated, there's ways around that.

But, by all means, do the control experiment. I would predict that you'll get a slower result than with your boyfriend, but not a ton slower. Assuming you make sure to eat the same meal, or very similar, anyway.

Just remember that it isn't 1:1. The air temp may be different by a few degrees, you may have had more or less sleep beforehand, time of day can make it vary. Clothing, textures of bed linens, etc. The boyfriend isn't the only factor involved. So don't expect a perfect result where the exact degree of reduction in time-to-sleep (aka sleep latency) is the exact same, or wildly different. You might not even be able to measure the difference since you didn't actually measure the time precisely the first time. You'll be relying on your perceived time to sleep unless you have the ability to read and record brain waves. Even watches and such with sensors aren't precise in detecting sleep. They get close, but only to degree.

You need a control experiment. Try sleeping with a heatpad without your boyfriend before you assume it's the heat pad.