HELP trailer sway almost killed us!

First question that comes to mind with me is "what are you towing with?" Short wheelbase vehicles like Wrangler and some others are more likely to have problems with sway and ALSO what kind of anti sway system are you using to hitch up? Pop up trailer are sway prone and having SOME sort of anti sway equipment is always a good idea. Usually something as low tech as a friction bar will work wonders at keeping the trailer tracking well behaved behind you. Speed, as already mentioned is another HUGE problem. I have NEVER SEEN any kind of tow able trailer sway while standing still. The further you get away from that rock steady state the more likely sway is to happen. Breaks are another issue but probably not relatwed to your sway but could make getting OUT of it difficult so I would make sure they are correctly adjusted and the controller is correctly set. Proportional controllers are best but even a timed controller should work when you hit the slide on it.