Apple Watch screen suddenly shattered

Glass doesn't break by itself. But if you think yours did, schedule an appointment at your Apple Store Genius Bar and show it to them. If the watch is still within its one year warranty and Apple believes there is a manufacturing defect (rather unlikely), they may cover it. If they do not believe it is a manufacturing defect whether it is within or not within warranty, the replacement cost of the watch, will be your cost.

To answer your question ... no, I have never had this happen to any of my Apple Watches. Not to say it can't happen, but I, personally, have never experienced it myself.

Regardless, depending on how long you have had this Apple Watch, and whether or not, you elected to get an AppleCare+ plan with it, will define what it may cost to get it repaired. The key here is having an Apple Technician examine the watch to determine if this a factory defect or not.

So, at this point, I suggest that you make a Genius Bar appointment at your local Apple Store or Apple Authorized Service Provider to have them take a look and provide you with your options.

Ref: Genius Bar Reservation and Apple Support Options - Apple