Can the "now playing" list be retrieved if a file is accedentally opened, losing list

I have accidentally clicked on an associated Windows Media Player file, so many times, destroying the list of songs on the "now playing" list? How do I go back to the previous playlist (unsaved) if I accidentally select a WMP file? How many playlists does it go back?

Actually I found a way to step back, but I can't seem to find it consistently. How do I do it?