Minecraft is glitching thru other tabs

Im trying to watch Netflix but Minecraft is flicking thru the screen, I do not have Minecraft open. it flicks for less then a second but it happens around 10 times a minute. when it flicks I can see the inventory and health, somebody is playing but its not me. they're holding a pickaxe and they're on two hearts. I don't know why this is happening but its annoying, I can't watch Netflix in peace 😞  have I been hacked or is it a Minecraft glitch? please help 🙂 ALSO its only when Netflix is on full screen!!