A moment when your mind completely locks up, and needs to be manually be set back in motion. Similar to a brain fart, but a brain stall can cause a long period of inactivity unless voluntarily EASED back into a conversation or thought process.
Person 1: "Hey, what are you watching?"
Person 2:"..."
Person 1: "Hey!"
Person 2: "Uhh, errr, wait what?"
Person 1: "Are you okay?"
Person 2: "Uhh, yeah, I just had a bit of a brain stall..."