Functional Hypoglycemia is a real thing. I did a high school paper on it back when I had a rotary phone and pet dinosaur.

At the time -- nearly four decades ago -- there was no known cause and the only useful treatment was diet and taking high doses of vitamins.

When glucose levels get depleted, the body starts drawing on stored stuff in the liver. The mechanism for releasing that is adrenaline.

When the liver stores run out, you have no further backups. So then you start waking up out of nightmares that involve running because your heart is racing in your sleep as the body tries and fails to access your depleted emergency stores.

I've never heard of it as a neurological diagnosis, but it is known to impact mental functioning and promote terrible anxiety.