Caged our of lucidity?

Title: Caged out*** of lucidity
The other night, I became lucid and began just walking around. (it being the first time I became lucid and had enough control to stay in it.) I was in a movie theater lobby, so I entered one of the theaters, but right when I walked in the door a giant metal cage dropped down out of nowhere and locked me in, the second the cage came down I felt the lucidity going away and then all the sudden was back to regular dreaming.
So I'm wondering what happened...
I think the cage just surprised me and I lost control, but if I was lucid why did the cage even appear?
And does going through a door in a lucid dream do anything....?

Going through the door doesn't really do anything unless you use to create new dream worlds.

Dreams are random. Things just happen, if it happens again just use your control and go through it, or break through it.

alright, I'll keep that in mind. Thanks!

yeah, remember you can do anything