Hi Dazned - I have had this issue for quite some time, sometimes it precipitates a raising of temperature and warmth but sometimes it's just a surge of 'anxiety' through my body, I also think it is adrenalin.
At one point it was sending me 'into action', by that I mean I was responding to it, I had to get up and was switched 'on' immediately and just racing adrenalin. I decided to just let it pass and as you say, it does. Now I don't respond and I stay in bed and deep breath or think of something else until it passes.
As far as my own hypothesis goes, this in my mind is definately stress hormones, rising and falling along with female hormones doing their thing. When we are asleep cortisol levels rise and fall and if we are low on cortisol, adrenalin is produced instead = panic. Cortisol natural goes up when we wake, I am guessing that if 'too much' adrenalin is in the mix, it would cause this hypervigilant state in the body. I'm not sure of all the mechanisms, thyroid function and adrenal function are under stress around menopause, so perhaps it's this?
Tips from me would be to only do light stretching/relaxation excercise in the evenings and unwind a few hours before you aim to go to sleep. Another tip that seems to help is to eat something small before I go to sleep, something with protein, a bit of cheese, nuts seeds - this helps to keep blood sugar stable through the night, which if not balanced adds to the whole crazy hormonal pattern going 'wrong'. Drinking enough water every day also makes a difference for me. Basically the 'stress' of hormonal changes means we need to eliminate stress somewhere else in our lives to remain on an even keel - I'm attempting this, but it's quite a task sometimes
Good luck
