Back in my yoof I too once took our Chippy to about 13,000 feet. The last bit took ages, and at that height the aeroplane felt as though it was balanced on a pin - way out of its comfort zone (as was I!). For some reason I felt quite vulnerable looking down from such a height - something I've never experienced before or since in an aeroplane.
I think I slipped off most of the descent. It was a long time ago and memory fades.