Hi and welcome to the Chiari forum.
Since u have a Dr that is somewhat knowledgeable....try to get them to do more testing to show what the issue is....so many Drs look at the size of the cerebral tonsil herniation and that is not Chiari, only the result of it....and like the description of Chiari 0 it is possible to have the smallest of herniations but much more severe symptoms then someone with a very long one at 13mm's....the issue is more if it is wide or obstructing CSF flow, so a CINE MRI to check flow would be a help...also ask about related conditions like Syringomyelia, tethered cord, disk issues, ICP, sleep apnea, ehlers-danlos....as they all can cause similar symptoms and issues....and can be over looked since the herniation is not where they feel it should be....sigh....
Once u get more testing get copies of it...reports and images on disk so u can easily go for another opinion....use the list we have posted in the Health Pages to research Drs....not all recognize Chiari 0....and be advised u may have to travel to get to a Dr....
http://www.medhelp.org/health_pages/list?cid=186