Change your oil. Try sunflower or sesame oil instead. Those are the two oils that are specified in the literature. I'd stop with the safflower until you get some other oils.
Are you doing this on an empty stomach?
Try another and let us know if this is better. It's amazing what kind of physiological reactions happen with swishing oil around your mouth. I'm sorry this is happening to you, but I find it fascinating.
Hang in there, and check back.