Floor camel-backing

Q: I have a lot of lift on my floor. I think it’s called camel-backing / camel backing; like, the floor is a little hilly in some spots as if the staples have come out and now the floor is lifting.

What is the cause? How do I fix it?

A: Is this something that has just developed? Is it possible you have a water leak and it is expanding the boards and causing it to heave?