Extensive Vibration In The Upper Torso With Shock Like Sensation Throughout The Body

I am a 39 year old male, 90 kgs, 175 cm tall. I exercise regularly and I am told, quite muscular. When I fall asleep (and only when I am falling asleep), my body, mostly upper torso, begins to vibrate from within. This vibration is extensive, typically lasting only 10 to 30 seconds, accompanied with an electrical shock sensation throughout my body. These episodes begin with me noticing my heart beat, which becomes loader and more forceful. But during the internal vibrations, my heart beat does not increase (I have checked my pulse on numerous occasions). Nor is it irregular. I have sleep apnoea, but have a device that regulates this. And, I am fully conscious at the time of these vibrating episodes. I can feel the episodes beginning, to the point where I am prepared to check my heart rate prior to the vibrating.