We were told by the pilot that the co pilot had got up to get a drink when the aircraft dropped at an angle of between 20 and 40 degrees, some one said 60 degrees.
At the time we were at 33,000ft flying on auto pilot. I was sitting right at the back of the aircraft and was suddenly lifted out of my seat as far as my belt would allow me, but others ended up on the ceiling. Apparently we were at negative 1.6g The whole event lasted around 40 seconds I think