The actions of the autonomic nervous system on blood vessels is called vasomotor.

http://en.wikipedia.org/wiki/Vasomotor



Drugs can affect vasomotor tone as well as endogenous biogenic amines like serotonin and bradykinin. Endogenous epinephrine and acetylcholine also control vascular tone.
And this article while complex does explain the role of serotonin in hot flashes:
http://docs.google.com/viewer?a=v&q=...D1BXON-YWJ7pqQ

And men also have hot flashes:
http://www.health.harvard.edu/newswe...-An-update.htm

It can be quite complicated. Women learn this during menopause, as vasomotor side effects manifest then. Called hot flashes.

Many people also discover as they age, that using a top sheet is not a good idea in bed. This prevents air circulation around the legs and feet. Using a light cotton woven blanket (not a soft pile type) may be helpful in winter. Also switching to jersey bottom sheet allows air to circulate around your body at night. Finding a fabric for jammies, that is waffle woven, is also helpful. Normally during the day we are upright most of the time, so we have 360 degree air circulation around us. At night part of us is blocked from the air, and that can create heat problems. If you use a tempurpedic mattress or top cover, it is worse as this traps heat.
We give off many organic gasses thru our skin, and this gets blocked when sleeping. I've read that about 100 compounds are excreted thru our skin daily. So having fabrics that allow air to move around us at night can be important.