Hi Lara,
This could be OSA better known as Sleep Apnea. During my Polysomnagraph, which is done over night at the hospital, I awoke as if from the dead. I told my Doctor that if I was going to have an MI it would have been during the five times this happen. I had to tell the tech no more.
Interestingly,I had my Epiphany the next day after my first Polysomnagraph.
I think added oxygen to my Amygdala, like stopping smoking and weight gain, was why I never experienced Dysphoria before. It was like a light bulb was turned on.
You also might have an undiagnosed Arrhythmia. A Cardiologist would order a 24 hour holter monitor to see if your heart is suddenly stopping during sleep. This is very dangerous due to formation of blood clots in the chambers of your heart, caused by blood pooling. Do you feel your heart skip a beat sometimes? Well, This is common and could be nothing, but the monitor will tell the Cardiologist if it is significant.
Good luck and fair leads.
Dahni