Baby shaking uncontrollably

So my baby girl is 8 months and this has only happened three times since she was born. Both the same scenario - she was dead asleep and in her car seat while I was driving and I parked to get her out. As I opened the door both times she suddenly woke up and was shaking uncontrollably, for like 5 seconds, and calmed down as I was consoling her. She was totally fine afterwards and awake/content. Her eyes never rolled back nor did she ever loose consciousness. So I don’t think of this as a seizure. I am going to mention this at her next doctors appointment, but I’m wondering if anyone else has ever experienced this with their little one?