Snaking

I've never experienced snaking before but 2 weeks ago I got into a very frightening snake 

The situation was overtaking a lorry up a long incline (motorway) on the decent I indicated to pull back in as I did not want to tow downhill at excessive speed but the lorry would not let me in BUT this is point of the posting I let off the accelerator but I didn't slow down and the snake started and it was a few seconds before I realized I was still in cruise control hence no slowing down so just a warning to any one with cruise control on downhill sections