I have the exact same symptoms as you. It’s such a relief to hear someone describe exactly what I feel on almost a daily basis.
I feel my nervous system took a huge hit after I had Covid. The stress in my life was/is high and the first very odd sensation I had that lead to these symptoms was a very severe migraine. Ever since that day, which was about a year ago, I’ve had these inner trembles which seem to stem from heart palpitations , along with lower abdominal pain, mostly constipation, brain fog and headaches.
I can’t get any solid answers out of my doctor or herbalist.
So I’ve chalked it up to more emotional and really working on mental health.