Hi...I think we all have gone through this part of the journey.....and many times it is due to the fact there are far too few Drs that are well informed and experienced with Chiari to really give us any answers....so they give what they think without really knowing.
Did you have a CINE MRI to check CSF flow?
Do you have copies of ALL the MRI's and reports? If not, request copies from the facility since they generally will give them to you without a cost, the Dr will charge you.Going forward always request copies of ALL testing including blood labs and reports.
Chiari symptoms cycle so they can come and go and sometimes it can be longer then you might consider , and many think it went away, then came back....it is always there, and for unknown reasons affect us differently....stress and our activities can also affect how these symptoms affect us.
Now the length of the herniation is not a reason to do surgery as surgery is done to restore CSF flow, until you know if you have an obstruction or not that will determine if surgery will benefit you.
A syrinx can dissipate , and this is something Drs monitor after a decompression surgery is if the syrinx size changes post op.....so if you had an obstruction that corrected it is possible the syrinx's size changed.
Now your headache can be Chiari or Chiari related.....so it is important to again have ALL related and non related conditions ruled out.
Having the right Dr is key as you have learned......they can not take something seriously if they don't understand it....