Search all your hard drives for files that end with .itl
That is the itunes database file that holds all the metadata like ratings, play counts, and your play lists.
If one of them has a fairly recent date, you might be able to recover at least some of your playlists.
Of course you will find one with today's date, but that is probably the new blank library.
I have
never heard of this happening while itunes was running, the entire library getting deleted spontaneously by itunes.
For the future, make frequent backups of that ITL file. Just like you would with any other important file on a PC that you can't bear to lose.
c/..../music/itunes is the default folder
iTunes Library.itl is the file name
I copy mine over to a USB stick about once per week, after I've done a lotf of adds/edits, and ALWAYS before an itunes upgrade.