Black screen with only top bar working (time,battery%)

When i switched on my phone, the sceen went black but only the top line bar was on, the bit where it has the time/ battery%. I try to turn off/on. Didnt work. It only went back on by its self hours later. So now im scared to switch my phone off. This has happened 2 times now. Can i do anything to stop this from happening again?

Also when my phone was on, i did get a error message something about processor not responding. does this have something to do with it?