If it happened all the time I would think it's the steering gearbox (spool valve). Since it's more of a surprise I would look at the EVO sensor.
At the bottom of and inside the steering column, just above the small u-joint, is a doughnut shaped sensor for controlling steering effort at highway speeds. When that acts up the steering will do as you describe. Connected to it is a plug with, I think, three wires in it. Disconnect that plug and see if the steering calms down.
Let us know what happens.