Hi there, this could be related to a vitamin B12 deficiency I have just started writing a blog as I have healed myself from this deficiency in early 2016 and I am keen to get the word out there as to the list of symptoms that come with a B12 deficiency incl brain fog and muscle weakness (incl eye muscles) and a sore neck; as well as the simple cheap cure that I found worked for me. I had difficulty swallowing, hence the name of my blog, but you will find good information contained within. Since I am new, I can't post my blog link here, but if you are interested try typing in difficulty - swallowing di christian (my name) and you should see a video with a link to my blog. If you take methyl B12 you don't have to swallow a pill as they are sublingual and you suck them to bypass the gut and get the full benefit, normal oral B12 pills won't work as well anyway. All the best.