Weird Black Square Glitch

So i was playing a Minecraft world with Jigarbov's Potato Addon with my friends and i snuck into where they were having a meeting with their Mutatos (one of my friends was a Mutato) and then i was in a hole in the room and then a was doing random emotes and i spammed faceplant at one point and then a translucent blacky-grey square appeared covering the bottom-left of my screen but the controls were in front and it was still translucent and also it didn't cover my entire control movey thing.