This happend a few years ago. Pulling towing a 5000lbs camper. Trailer brake gain instantly went to 100%, forward collision warning blaring, ABS fighting my 2 feet standing on the pedal, wife hitting my chest and saying "your going to hit them! YOUR GOING TO HIT THEM!" "Yeah, probably, brace yourself". Luckily I saw the red brake lights just past this car and was already moving my foot over to brake. Just didn't expect my stopping distance to be cut in half suddenly.