I can tell you from my experience that my onset was slow and then very rapid. It started with heart palpitations, insomnia, digestive issues, orthostatic hypotension, vertigo..
My left foot and leg would go numb from sitting positions and my left hand had a vibrating feeling. This all lasted about a year and then suddenly last September, I started have shooting nerve pain from my neck to my arms and I couldn't move my neck. By November it spread to my legs and my whole body. The pain was excruciating, buzzing, vibrating, muscle spasms, tinnitus. I couldn't move or stay still I was a terrible mess.... and the autonomic symptoms became worse. So, I was like this for 4-5 months. I couldn't drive, or do anything. Could barely eat. By Jan/Feb I could drive short distances very carefully. I am now functioning, but it is hard. Some days are better than others. When I look back though- I'll take it.