A much better three word description than Donsboig's "on your front" would be "the recovery position". The important aspect for sleeping isn't the position (I slept only on my back for the first two months), it's the hard surface underneath a thin foam mattress or a mattress topper.
If the symptoms were caused by SM, the diagnosis of proprioception dysfunction would be negative because a positive diagnosis requires an immediate and demonstrable improvement in muscle tone in the neck after wearing specific prism lenses. If the origin of the symptoms was SM, then this would not happen. I agree completely that these symptoms need not only come from proprioception dysfunction. I also note that the prism glasses do nothing to help a patient's sight or any other problems with their eyes.
Thank you
@lenora for sharing your story, and thanks too for not berating. I've not joined an ME/CFS forum since recovering in 2018 (after first falling ill in 2014) precisely for fear of what the tone might be, and I'm grateful that even in raising an alarm, you did so in a genuinely nice way. I stumbled upon this thread and joined the forum in order to answer a few questions that had been posed in this thread, hence my rather long post above. My observation here is simply that if a patient with symptoms of ME/CFS is diagnosed with proprioception dysfunction, then the treatment has shown positive benefits for several patients and a spectacular recovery for a lucky few (me included). I make no claim whatsoever beyond that, and certainly no claim for someone who isn't diagnosed with PDS. I'm a pure mathematician, not a medical doctor or an opthalmologist, but I was so excited to discover that my ME/CFS had a purely physiological diagnosis and treatment despite several doctors telling me that there was nothing physically wrong with me. After I recovered, I simply wanted to find out if I was the only person with ME/CFS who also had PDS. I was even more excited to discover that I wasn't unique! Thanks again, Alastair