You say "shaking". Is it shaking or vibrations? There is a difference. I sometimes have a shake in right hand like when you're pressing on the nerve and it will quiver and shake but I'm not pressing on it. These vibrations occur ONLY when lying down in bed and only AFTER I have been asleep. I looked up "diaphragmatic flutters" other day and it gives a little more detail as to what is going on and again, it mentioned the phrenic nerve. I'm on the right track. I'll keep searching until I find it or a doctor willing to help us find out. I take BP meds and also a beta blocker for my PVC's, heart palpitations. Sometimes I'd have a dream and wake up with heart racing and pounding but I think that may have been part of the sleep apnea.
If you are waking up several times during night, I'd be asking, why? That's why I did the sleep study and found I was having 31 episodes an hour of sleep apnea and of course you wake up. The sleep study I did with the nasal piece, I had 1 episode but also found I didn't have the vibrations for a week and a half after and slept very well. I now have the machine, which medicare pays for, but I use it the minimum 4 hours BEFORE I go to bed and I sleep anywhere from 6-8 hours a night now. I might have the vibrations 2 out of 7 nights but they are very mild. I just love it when I sleep until 5:00. My next step would be a sleep study if I were you.