Mellen, since you said you're post-menopausal, what exactly does a hot flash feel like? Do you get hot like you're in a hot room, or is it hot like the heat is coming from the inside out?
It's a sudden sensation that the temperature in the place you are just shot up 20 degrees with high humidity. At it's worst; An adrenaline surge, that "uh-oh" fear surge sensation in your gut, rapid heart beat and you see specks or stars, arms and face/chest feel numb, as if just when about to faint...which sometimes does happen, too. Hot flashes also happen with some severity on occasion during menstruation, though it's rare for most women (I only had one really severe almost-passing-out hot flash while on a period).
From what I've read, the theory is that the brain gets used to using estrogen, along with other hormones and neural chemistry, as part of the virtual body temperature "thermostat" control system. When the levels of estrogen swing wildly, during a period, pregnancy or menopause, that's equivalent to signal disruption or line noise, and things go haywire for a bit. During menopause, it just takes a while for the virtual thermostat to work reliably without the estrogen component, almost a "learning" process.