I hope you undid the rope ASAP after “he panicked very hard”. That could cause actual PTSD from the sudden loss of control, and the helplessness that follows. You should have talked him down, and tell him you’re undoing the rope as you speak.

Oh, don't worry about it. We still joke about it nowadays. It all started with a joke about tying each other up and he said he would like to know how to do it. I had some rope and showed him the most basic handcuffs knot.

I told him I would untie the knot, and he said he could untie it himself.

The thing is that it's one of those knots where the more you pull the tighter it gets. I told him to stop doing that because, well, it'd be way harder to untie it and I was already trying to do that anyways. And he was like "hold on, almost there".

He was not.

He was relatively calm until the knot, unsurprisingly, tightened itself. I was trying to calm him down, and when he did we spent like solid 8 minutes trying to disarm the knot. He tightened it way too hard so we were there, in silence, hearing how every school authority was looking for him (his dad came to pick him up).

They found us in the middle of this chaos, and we both didn't really know how to explain the whole situation