Our bodies are marvelous. They make thousands of adjustments in a multitude of interlinking systems every second. Like any complicated system, it can be tricked. We usually use medicines to trick those systems but sometimes there are valid, alternative (free) methods for some maladies.
Warm hands cause the capillaries in the hands and fingers to dilate and pass more blood. That results in a minute drop in blood pressure. If the person is calm and resting, the body will contract other capillaries to maintain homeostasis. Among the first set of capillaries in the hierarchy are the capillaries in your nose.
Your nasal tissues shrink. Your nose un-stuffs.
How do you make that happen?
In a lab they direct the subject to place a thermometer between their hands and to look at the temperature. That degree of thinking defeats the purpose when one is trying to go to sleep.
I prefer to hold my hands close together (about a half inch apart (10-15mm)) or to hold them close to my thighs. Then I either visualize a candle between them, or that I am holding them in hot dish water or that I have buried them just below the surface of hot sand at the beach.
I think human flesh must be exceptionally reflective of IR radiation. I can hold my hands a half inch from my thighs and feel much warmth in my hands. Or I can hold them against my thighs and they will get cold because the surface temperature of my thighs is lower than that of my hands.
Once you have your hands all toasty-warm, do the same thing for your feet.
I am not afflicted with headaches, unless I drink too much cheap, red vino. But I have been told that this method can ease certain types of headaches as well.
I cannot speak to the effectiveness at reducing stress or alleviating headaches, but is sure eases stuffy noses. And Mrs ERJ love reteaching me the benefits of plunging my hands into hot, soapy water when my hot-hands reference needs recalibrating.