Earlier today (Monday) around 2:30PM, I was on approach to ANC in a DL 752, when we suddenly encountered severe turbulence. It was crazy. Thankfully, no one was hurt, because we were warned of moderate turbulence in the area and everybody was buckled up for landing. But no one was expecting the turbulence to be severe. The pilot said after the flight that at 7000 ft, we had suddenly encountered an 80kt tailwind and had subsequently dropped at least 500 ft. There were also at least 2 or 3 more sudden drops. Everything in the cabin had flown up to the ceiling and was deposited far away from its original place. I got smacked in the head by a book that had come from 3 rows behind me. My small carry on, which was stored under the middle seat, since it was empty, had somehow freed itself from under the seat and flew forward a few rows and ended up on the other side of the aisle. During one of the smaller drops before the huge one, the lap baby in front of me was temporarily airborne. Thankfully, that shocked the parents into keeping a better grip on her. All in all it was quite a scary situation, and I'm still somewhat unsettled.
So now I have a couple questions. How often does severe turbulence occur, especially outside of thunderstorms/wake turbulence? Also, what happens in the cockpit during such turbulence? I understand that you're supposed to maintain attitude, and not worry so much about altitude, but what is there to do when the plane drops like that?
Also, just in case anyone thinks I was exaggerating about the severity, here's the PIREP from my flight.
ANC UUA /OV ANC180005 /TM 2330 /FL070 /TP B757 /TB SVR