What Causes Double Vision?

About 7 yes ago I started seeing double, side by side. It was really scary, never had anything happen like this before. It countined over about two years off & on, during this time I was pregnant with my youngest, have had everything checked from my sugar to my thyroid. Didn t have any symptoms other than double vision. Ended up going to eye Dr., he sent me to Neuroligist, had MRI done & nothing everything was good. After that I stopped having double vision until presently, which is seven years later. Out of nowhere one afternoon I had double vision again, no morning or after effect. Only lasted up to 7 min. Max. I have a apt. With a neuroligist in seven days & am very scared.