iPad screen randomly flickers after more than 1/2 hr continuous usage

My ipad fell from a height of 3 feet, initially I didn’t notice any problem. But recently If I use the ipad continuously for 30min, the screen starts pixelating, random colored lines and blacks out. I have to wait for 1 hour and again it starts working fine. I don’t think the problem is with the LCD, as it works flawless for 30min and blacks out.