I can't see my cards in my lists...I typed a shortcut by accident

[Irene Duma]

Hi, I miss-typed and must've hit a keyboard shortcut by accident, and now the  Lists on one of my boards have all shrunk to be just one little box at the top, and all it has in the box is the Title of my List,  and under it it says the number of cards under it: e.g.  "4 cards" - 

But I can't figure out how to get the view to look regular again, and I can't even open these cards!

What have I done? 

is there a History or Revisions to go back to a previous version? 

What kind of view is this? and what is it good for? 

Help! yes, I hit z a number of times. I looked in the activity, I see nothing.

[Irene Duma]

I found it in a Facebook Group for trello. It was a filter.

[Irene Duma]

anybody?