The fear of being locked in an enclosed place.
Jakob's got it.
I think it started with kindergarten recess, where the door automatically locks behind them when they go outside to play. And now the fear has spread to his bedroom door. My kids have always slept with the door shut (note: not locked, just closed), in the dark. But lately...
"Mom, will you please leave the door open and the light on? I don't want to get locked in my room. The door gets locked and it sticks together like this" (clapping hands together and pushing them against each other).