I was six or seven years old, attending a small school in a small city in East Euroope still rebuilding after the Second World War. The school had normal classrooms and the gym was the courtyard, but there was a largish meeting room.
One day, I'm given some schoolwork and am absorbed in it. Suddenly the teacher says my name, and I look up and realize that I'm the only kid still in my class. The teacher tells me to stand and leads me to the meeting room. She opens the door, and the lights in the room are dim, with music playing. All the pupils my age are dancing in pairs.
The teacher leads me to one girl from my class, and arranges our bodies and arms in a tango pose. I feel the girl's cheek pressed against mine and shriek and dash out the door. An adult from the school catches up with me in the courtyard and leads me back to the class. Later, the other kids return to class, and the whole thing is never mentioned by anyone.
This isn't a delusion. It really happened.