Hi u may want to check out the Chiari Malformation forum here on MedHelp as low lying tonsils can indicate u have Chiari or a related condition....even with low lying tonsils u can have Chiari symptoms.....
With Chiari we can have pressure HA's from simple things like laughing, crying, shouting, and doing nething that causes us to strain....
How long since u received ur low lying tonsil DX and were u in a MVA that may have caused it?....
Do u have copies of ur MRI and the report?
Here is the link to the Chiari forum -
http://www.medhelp.org/forums/show/257?camp=msc