Others may have a better explanation. When I first started OPing the oil got thin relatively quickly. Over time it seem to maintain a thicker consistency. Recently, with the pollen season in full force, the oil has been thinning out again. I also did a Liver Flush two weeks ago that resulted in braking out in hives. The OP has eliminated the most severe symptoms, but the oil gets very thin.
I'm allergic to bee stings, and the first reaction is hives. The most severe being in places where I sweat (primarily crotch, arm pits, and between my toes and fingers). When I was in Vietnam I was stung 17 times in the face. I eventually lost bowel control and consciousness. Since that time I've been allergic to even a single bee sting, but none as severe as that first time. I think the Liver Flushing is clearing some stuff out of my liver related to the bee venom. The question I have for myself is it related to the last time I was stung 6 years ago, or to the accumulation of bee toxin over the years.
There were a lot of toxins released into my system after that liver flush. The symptoms are significantly reduced with OPing, but the oil has become very thin again. I will also say, that usually by this time of year, I'm one of the most miserable SOB's on the face of the earth from pollen allergies. This year I've had some sneezing, and itchy eyes after being outside all day, but other than that it's been a good spring. I can actually work in the garden again. Even though we have had a lot of rain, the pollen season this year is particularly bad. When I started OPing last Fall many people mentioned the elimination of allergies from oil. I must have been from Missouri in a previous life, because I was skeptical. However, as far as I'm concerned, the difference is equal to how far the East is from the West. Again the oil started getting thinner when the pollen started hitting.
So..... I would say if it is thin, you are pulling a lot of stuff out...bacteria, viruses, toxins, etc. All that stuff probably breaks down the chemical composition of oil. As the toxins, etc. die, a chemical reaction occurs that breaks down the viscosity of the oil. Sort of like what happens to your engine after 3,000 miles if you use inexpensive motor oil. If it's thick, you're probably relatively healthy. However, I wouldn't stop. If you're not seeing changes, it does not mean it's not working. I saw some relatively dramatic changes in skin, gums, tooth pain, and ear pain the first six weeks. Once all that stuff was cleared out the oil became thicker, and I didn't see any additional changes outside of my mouth feeling dirty if I didn't OP for a day.
This really doesn't answer you're question as to why the oil thickens then thins during an OP session. I've never had oil get thicker than what it was when I first take a slug of oil. I suppose you could experiment. Maybe find someone with the worse dental hygiene imaginable, make out with him/her for an hour (make sure your tongues extend deeply into each other's mouths), immediately OP, and see if there is a change.
Hope this helps, and keep me posted if you try the experimentÖ. the details will be critical for an analysis.