I am so glad to see others with this!! I felt like I was crazy, lol!!! I’ve learned a little about the vagus nerve, and wonder if it is that? With my panic attacks, it’s like my body misinterprets the messages, being received from other parts of the body, so it exaggerates the feelings for me.. I don’t think that there’s a specific fix for it, except to go and have a bowel movement.

I have been having this SEVERELY for the past couple of years. After researching it along with my other symptoms (don't want to get off track here) I found that This may be a symptom of some physical conditions working together against me. i will elaborate:
I have had much bone removed from my legs in the past. To where I do not have much left of my femurs (mostly metal) This is where the majority of blood is produced.
My blood oxygen levels go down when I am at rest. Never been checked when just about asleep but probably very low.
My blood pressure has been steadily dropping for the past 6-8 years. To where my pain specialist said that something needs to be done about it.
I have some kind of crazy chronic fatigue or fibro myalgia that has defied doctors for the past 30 years.
Recently been waking up from deep sleep in terrible panic, like I am dying.
No other panic symptoms.
I get so sick and fatigued an hour or two before bowel movements that I have to lay down (and writhe in pain) Along with this is dizzyness, brain fog etc.
I have read that a woman who was struggling with several similar symptoms was diagnosed and treated for "Hypovolemia". This is a condition of low blood volume. It is rare especially when not associated with obvious blood loss. BUT
All of the symptoms align here. Consider:
Panic waking from deep sleep... we have all heard of people choking to death on their vomit or bile when on drugs or very drunk. I used to wake up choking on bile when I used to consume milk products. One wakes up when choking or the system is about to shut down for some reason. I believe that violent waking from deep sleep in a panic CAN WELL BE associated with the body's response to a lack of oxygen. Maybe some do not have this semi automatic reaction but some do. Me do!
We know that when our bowels digest they use more blood causing the brain to be a bit starved and making us sleepy. If this effect is magnified it could instead cause sick feeling instead of simply tired. Hypovolemia would certainly magnify this situation.
So that is what I think is happening with MY ill feeling before bowel movement AND my wake up in a panic attacks. The combination of low blood volume and low blood oxygen is causing ME much of my problems. I wanted to share so others may gain from this observation.

I believe I have found the answer. I get very sick, dizzy and weak 1/2 hour before bowel movements. I also wake up from occasional very deep sleep with a panic feeling like I am about to die. (not panic attack). I also have CFS or some unknown thing (for over 30 years) This is what I believe is happening. HYPOVOLEMIA. There are studies now associating CFS with hypovolemia and the "waking up just before dying" is a symptom people have in common along with this terrible distress while the blood goes to the bowels and leaves the brain. I liken the feeling to years ago a couple times I drank enough alcohol to get the "spins" This feels exactly like the spins.