I understand now that you were doing the oil pulling with coconut oil.
First I hope you were using Virgin Coconut oil. Hydrogenated coconut oil may not be good.
Second, you did not mention what you did after oil pulling. Because you should rinse your mouth with warm water salt water to really rinse the oil and brush your teeth afterwards.
Thirdly, does this happen every time you do oil pulling or just once? It could be a detoxification effect you were experiencing which should go away after a few days or even weeks depending on how your body has been keeping your toxins. You may slow down a bit.
Fourthly, do you have dental fillings like mercury fillings etc? Remove them! That can be the main reason.
Lastly, there should be no side effect for oil pulling except detox effect.