If you are cooped up somewhere, you are in a small closed space from which you cannot escape, or you feel as if you are.

I hate being cooped up inside working when it's a sunny day outside. 我讨厌在外面阳光灿烂的时候自己被囚在室内工作。

It's such a tiny office - don't you ever feel cooped up here? 这间办公室这么小——你不觉得有种被囚禁的感觉吗？