Had a similar scenario myself on the M5 back from West Brom to Halesowen after work recently. Very wet on the motorway, not really enough to Aqua plane too bad though. Was in the outside lane doing a steady 60-65, lorry however decided it would be a top idea to stick in the middle lane doing same speed. Some twat in inside lane nipped in front of the lorry causing him to brake quickly ...
Never have I sh*t myself so much in a car ... And I've been in two crashes, one big one.
Lorry having slammed his brakes on snaked HARD towards me in outside lane! Eased off the gas a bit, and dropped it a gear rather than brake hard myself and risk snaking myself. Thankfully the driver caught the oversteer well and stuck it. Genuinely thought I was going to be one of those fatal car crashes you see on the motorway that day.