Sounds like you need to have an Oesophageal Manometry test done. This will test for oesophageal paralysis or dysmotility. One of my earliest symptoms was difficulty swallowing and a feeling that food/tablets were getting stuck. An extension of this is Gastroparesis (paralysis of stomach) which I also have.
Many M.E. people complain of gut dysmotility so it is really an extension of GI tract paralysis/dysmotility.
I too had an Esophageal Manometry ( along w/ endoscopy and a barium). This was a miserable test, but the most helpful. It showed that my
peristaltic waves are all out of sync. Of course, no real reason for my case was able to be given. I would guess ......... ME ;-) well they are
muscle spasms of a sort. Have lots of those elsewhere. Also, it is not uncommon for the cause to be unknown. It can run in families.
However, There are some things that are known to trigger this condition, so it's good to have the test(s) to see what they can find. There are some treatments for things known to trigger this dx and are worth giving a try.
And as Francelle points out, it can be an extension of other gut motility issues. (A good gastro will want to throw in a colonoscopy too.)
Here's a link to a site that I have found a very good resource to understand gastro tests and disorders. At least a good starting place for
the later.
Jackson Gastroenterology
I hope you find out what is causing your problem and can get some relief.
Mine comes and goes in severity.