Self driving was maintaining vehicle. Looked at roadway before reaching down to passengers side for water bottle. The weight shift in the seat turned the self driving off immediately while turning sharp left. The Tesla Model Y crossed the left interstate lane barely missing an 18-wheeler. Drove 80mph in the central ditch, branches, and rocks. Car was still in drive, and rolled up to roadside which was covered in dust. The two eighteen-wheelers that I cut off then Drove away, and drove tesla to next exit to see damage.(dashcam footage available.)