My Iphone 11 closed and didn’t open

I was watching tv and I wanted to see what time it was then I get up to grab my brand new Iphone 11 and it didn’t open . I freaked out because it is 5 days old. Then I put it to charge and still didn’t open, so then my mom called me and thats how it opened but my question is why did it close and didn’t open? Someone help me.Thank you for your time!