HI...it is both, but inter related....let me try to explain......there r many related conditions like Ehlers-Danlos Syndrome, many with it also have a hiatal hernia and with that u will have GERD...EDS is a Chiari related condition....so in that way it is inter related.
That said, I would cough all the time and had post nasal drip which is sinus related and that can be affected from the overcrowding of chiari...post nasal drip can also cause GERD.
And ne laughing I did would lead to coughing and gagging....and I am not sure if it was mucus related or just chiari related.
Do follow tips to modify ur diet and life style...elevate the head of ur bed etc.... to help with these issues. And a swallow study is usually done to rule out ne other possible condition or issue.
U can go to a GI dr to make sure 1- that u have too much acid, having too little can cause many of the same symptoms and u can not tell with out testing which it is.
With diet and lifestyle modification u can help....but do get checked.
We do have a GERD forum if u would like more info from the Health Pages there-http://www.medhelp.org/forums/GERD-Acid-Reflux/show/333?controller=forums&action=show&id=333&camp=msc
If u have ne other questions ..please ask here too : )