Hi...I can totally relate to your frustrations with Drs and felt the same way more then a few times over the years....BUT, it could be you have been to the wrong Drs....I found once I was with a Dr that was a true Chiari specialist I got more answers and understood what was really going on with me.
Begin tonsillar ectopia basically is a label Drs put on a herniation they feel is not affecting you, but if you were not affected why were you to see them in the first place....sigh...
Chiari 0 is when a person has Chiari but the herniation is not evident....Chiari is a malformation of the skull....it is not the herniation.....if you have a herniation and no Chiari then they call it tonsillar ectopia.... meaning you have a herniation of the cerebral tonsils.....Both can cause similar symptoms.
Site of nerve impingement determines symptom location
Sustained contact between extruded disc material and a nerve root is called impingement, also known as a pinched nerve or herniated disc. There are eight sets of nerve roots associated with the cervical spine, annotated as C1 to C8. Most annular tears within the cervical region occur at the C5 to C8 levels. The areas of the body affected by the pain, tingling, numbness or muscle weakness caused by nerve impingement will depend on the location of the annular tear, as described below:
C5 – pain or mild numbness in the shoulders, deltoid muscle weakness, reduction in biceps reflex
C6 – radiating arm pain, biceps weakness, weakness in the wrist extensors, reflex reduction in the muscles of the forearm, numbness in the thumb
C7 – middle finger numbness, radiating arm pain, diminished reflex in the triceps muscle
C8 – loss of function in the hand, pain or numbness on the outside of the hand, diminished reflex in the hand muscles.
source-https://www.laserspineinstitute.com/articles/annular_tear_articles/cervical/438/
With Chiari we all may have very different issues/symptoms.....so your palatal myoclonous could be something unique to you....and not a typical Chiari symptom.
As for your headache you didn't say if anything tends to trigger them....laughing, coughing, sneezing, or any strain.....??