Yes, you can have permanent damage if you wait to long. Have you had a csf flow study? One NS blew me off until that showed blockage.. Then everyone listened. How frustrating for you! You need a new NS.
Hi and welcome to the Chiari forum.
Can you clarify what you mean by severe symptoms. Many have breathing issues, drop attacks, seizures etc...
There is more testing that needs to be done to check for a CSF obstruction, and ALL related conditions.
Unless your symptoms change, you should be fine to wait to see a Chiari specialist.