I have had that. It was strange. I think I was fighting something...either an illness, or detoxing, or allergies or something like that. But magically, every morning, it would just disappear after pulling.
It happened every morning for a couple of weeks after I was pulling for about 4 months.
I have no idea why, but it never turned into anything.
My opinion is that I was run down, and I think that the oil pulling was causing my body to start dumping toxins. I had been doing a bunch of cleansing, like Liver Flushes and colon cleansing. I consider this my healing crisis. When it was over, I felt fantastic and didn't think about it again until you posted.