Dad (87) flew into a rage, hit me/yanked my arm. I'm afraid of him now. What to do?

We just upped his meds due to his high anxiety. We were waiting in the car, while my Step Mom went into the bank. He became enraged because I didn't turn the car off soon enough. I was sending a text to work & didn't do it soon enough. It was remarkable how quickly he came up over the seat to hit me, wrenching my arm and grab for the keys. I was so thankful that I had taken my seatbelt off, which helped me avoid him breaking my arm! I was stunned that he went from calm to absolutely enraged so quickly. We move at a glacial pace normally! He is so strong! I also was afraid that by trying to defend myself, I would end up at fault. I still feel I MUST not allow him to hit me. He HAS threatened it before, but I never thought he would actually do it! I must be so nieve! I don't wish to medicate him any further. Now, I feel anxiety around him, because I never know when he might fly off the handle and hit me again. He is SO strong at 87, it really surprised me!