Originally Posted by: hunter1801I'm changing the strings for the first time on my classical guitar and when I took them all off, the nut just slipped out. It wasn't glued or secured in any way.

The nut should absolutely be glued on securely. I recommend a bottle of hide glue. Consult a pro if not confident in your ability to fix.

FWIW, the bridge saddle (bar) on many classical guitars is not glued, attached or secured. And, of course, it will fall right out of the bridge when the strings are removed.