Vessel turned around

[Grottie Yachtie]

Hi, I own a 43' Tasman elite catamaran and on a solo trip from Sydney to cairns, Qld. It was new years day and I was between Bundaberg and the town of 1770, I was stuck in heavy seas, about 45kts, I had the main tucked away with just the Genoa out, I was streaming a warp of 200mts of 16mm rope with my dingy anchor shackled to it, on a bight. It was about 1730hrs when a larger than normal wave hit me and spun the boat around facing the way I had just come before I had a chance to do anything. The boat was on autopilot at the time and I was beside the wheel, but it happened that quick I couldn't do a thing. I was not hurt and the vessel was not damaged, I just started one of the motors, turned around and kept going. What I would like to know is how did it happen especially when I was dragging a warp and only under headsail? Has this happened to anyone else and what else could I have done for this not to have happened.
Would appreciate any feedback.

Grottie Yachtie