Its apparent from reading your post that you there's something going on in your neck, and your symptoms are a little worrisome. Be careful with Chiropractic manipulations of the cervical spine, they can often make you worse, and in some instances have disastrous results.
Panadeine forte and neurofen plus are really not strong enough for the type of pain you're having, I know I've experienced it myself.
Even if your cervical and brain MRI's turn out to be normal, you need to find a Doctor that will treat your symptoms. All problems are not detectable on scans, that doesn't mean that the problem doesn't exist.
I"ll give you a link to the Chiari Malformation forum, there's some great people over there, and they'll gladly help if they can.
http://www.medhelp.org/forums/Chiari-Malformation/show/257