Opening the most recently hidden buffer in Vim

A开发者_如何转开发ssuming that I have two buffers. One is NERDTree, the other is an actually file I'm editing. I accidentally open an another file from NERDTree and the new file hides the previous file I was editing.

A similar case occurs whether I use NERDTree or not.

How can I bring back the previous state by opening the mostly recently hidden file? I'm using the word "hide" because this is probably not "closing".

I use ctrl-6 to switch back to the previous buffer in the window.