This is an interesting discussion and one I can relate to. I've experienced these internal tremors or internal vibrations on two separate occasions in my life. Once two years ago that lasted for about a month or so and now currently where they've been lasting for the last couple of weeks. Both of them seem to have been triggered by a family health scare so I believe they're brought on by stress/anxiety in the sub conscious mind. I've been waking up almost at the exact same time of night (3:30 a.m.) and when I try to go back to sleep my upper body 'vibrates' inside. Oddly, if I open my eyes and become more awake/alert, they instantly disappear (like snap of the finger disappear). But as soon as I close my eyes and start to relax/fall asleep they start again. Heart rate is perfectly normal, BP is normal (I have an Omron BP machine at the floor next to my bed). I feel like it's sub conscious because I don't go to bed actively thinking about anything negative, I don't feel anxious or stressed when I go to bed. But the fact that it seemed to have again been triggered by a stressful family health scare leads me to believe it's somehow rooted in my sub conscious. The thing that stinks about that is I don't know how to 'beat it.' I've tried Melatonin to sleep better which hasn't worked now 5 days in. I even tried to take Nyquil to try to 'knock myself out' and sleep deeper and that didn't work. I've tried some teas for stress/anxiety, some mood boosting supplements too. I've also tried brief meditation, stretching, and ensuring I get enough fresh air. Thus far, it's been a whole lot of nothing. Next up is Magnesium Glycinate to see if that helps. I'm currently not overly concerned (more annoyed) since they're not accompanied by any other symptom and literally disappear when I open my eyes. I often wonder if it has to do with hypnagogia and sleep states being interrupted by sub conscious anxiety. Curious if anyone else has any other thoughts/ideas or experiences like mine. It's just very weird to me that it only happens at night, only around 3:30 a.m. and disappears instantly when I open my eyes and wake up more completely, yet returns then when I try to fall back asleep.