I used to have the same thing. Exactly. When I would start to doze off, my body would shake so much that I thought I was having seizures.
After many years, I attributed mine to something in soft drinks. Maybe a chemical or the amount of caffeine. But I also methodically worked my way towards a more healthy lifestyle. However, I got rid of them, but I still have a less volatile form of them. I do still have some caffeine on a daily basis. I never thought much about it until I read your message. Maybe you are super sensitive to caffeine because of your adrenals.
My endocrine doctor just tested my cortisol level and it is at the bottom of the range of normal. I also have hyperthyroid problems.
I know I wasn't much help. But I used to go to the doctors and tell them I was sick and they just patted me on the head and sent me out the door with no help. That was 1989. I figured with such a horrific symptom surely they would find something wrong with me, but they never did.