Reality dissociation.
I went through a period in my very early twenties when I more or less constantly meditated. One of my meditations was to look at everything I saw or thought, and state firmly in my mind, “this X is not real.” Your mind is highly impressionable to stated thoughts like this and if you keep it up, eventually you’ll actually start to believe it. The world achieves a very unreal ‘air’.
Another meditation I did around that time, one a bit more difficult, is to throw out all thought as it arose. The way I did this was to state affirmatively, “I don’t know anything,” to any sort of thought or question or musing or anything that came up in my head. I called it my “newborn” state. I was learning thing, and then throwing that learning away immediately as I learned it.
This made dealing with people, well, problematic. At first I tended to stop doing the exercise for the purposes of a conversation. But my experiment wouldn’t let up, so eventually I worked out how to keep the newborn state even while conversing. I stopped doing this when I suddenly realized that where it was pushing my mind, continuing to do the exercise wasn’t going to keep it going there. So I came out of it, and tried to make sense of the last few days.
When you’re doing strong meditation, you’ll find yourself getting the urge to take the meditation off of the couch and out into the world. This can feel dangerous and weird, but generally the fears are overblown. The same reason you fear it is the same reason you need to do it. Doing it will remove the mystery, and you’ll just know when to stop.