I have had internal tremors for a year now. Exactly as described here - only when falling asleep (they wake me up) and when awaking in the morning. I have had to go on a sleep aid to sleep which I hate but it’s better than no sleep.
From my own research and situation, I am convinced it is a symptom of an overactive sympathetic nervous system/compromised vagus nerve. I believe this because the internal tremors started out a few months after I had multiple traumatic events related to my heart. They started slowly and progressed to every night. I find the intensity is less if I have a trap and neck massage (stimulates vagus nerve) right before going to sleep. I am curious about the breathing component and will work on deep breathing exercises also and see if that helps. I am hopeful that if I work on healing my vagus nerve and deactivating my sympathetic nervous system through holistic means, I will eventually get relief from the internal tremors. I am so grateful to have found this nice to know I am not alone.