Jumps or jerks when putting on drive and reverse.

Jumps or jerks when putting on gears drive and reverse, drives fine. Did this four days ago and has not done it again. At first it felt like a transmission problem but now I'm not so sure. When it did that I had just driven it for 40 minutes. Then I was parked with car still on for another 2 minutes then when I put on reverse it jumped. I pulled out of the parking spot then changed to drive again it jumped. I changed it to neutral and didn't jump. Switched gears a few. Times to see if it would stop but didn't. Left it there and when I came back with mechanic it didn't do it again. He told me it was ok to drive and to bring to his shop if it did it again.