Ipad Pro screen crack by itself?

The past couple days I have been using my ipad and it has been working fine, screen had no cracks or hairlines fractures that I or my partner could see, I set my Ipad up on the charger and left it on my night stand all day while I was out. Then came back and still, no cracks. I put it down on the table (on its back, in a secure case) to eat and then I go to use it and notice a crack. I didnt drop it or anything, so I was wondering if heat could cause this or what other people thought about this.