I recently developed a version of this, I am 50yo male, and a month ago I started waking up to big, shiver-inducing adrenaline spikes, usually coming on gradually in the 30-60 minutes after waking around 5 or 6. I ended up seeing a doctor and even ended up in the ER for it. It plagued me from April 25-30, then it subsided for 3 weeks, and then came back in force May 20-25 (today) and I have no idea why it abated.

Symptoms are severe shivering, dread, urge to move around, urge to seek help, very sweaty hands and feet, dooming/health anxiety, frequent urination, same basic symptoms of intense fight or flight being triggered without a good reason. It started out happening gradually over an hour after waking naturally in the AM, lasting from 3-4 hours each time, and then now it has progressed to actually waking me up at 1:30 am, 2-3 hours into sleep.

Of course, blood tests showed nothing so I have no idea how to proceed, other than working on my coping and wondering what made it go away for 3 weeks. I do have a hydroxizine scrip which helps, but the trauma of waking up to fight or flight is formidable in itself so I worry this kind of thing can be self-reenforcing if the cycle is not broken. Also no idea why it moved from "after I wake naturally" around 5am, to "now we're going to do this after your first 1-1.5 sleep cycles."

I'm getting therapy for it, but as kind of a skeptical person, I'm reluctant to jump to "emotional causes," like unresolved trauma, because my work and family life are happy and relatively stress free, and I note that I feel pretty otherwise calm and unworried now when it happens--except for the fact that it feels "like an EMT has shot me full of adrenaline to restart my heart," which of course ruins sleep.