It could be anxiety, anxiety can manifest itself in weird ways. I used to wake up from dreamless sleep with sudden panic attacks, extreme N* and uncontrollable shaking. Every time I was sure if I moved I was going to V*. I would stay shaking and feel N* for hours until I burped a lot and got rid of the N* feeling and the shaking would eventually fade away also.
So it def can manifest itself into extreme physical symptoms.