As I was driving the automatic emergency brakes went off and stopped me so hard and fast that I feel like I got whiplash. The seatbelt yanked me backwards, smacking my head against the headrest, I have an instant headache from it and my neck and shoulder still hurt 20 minutes later. It scared me and my child half to death, my heart was pounding and I could have been rear ended. I was driving about 40mph and was in no way in any harm/needing to break (specially this hard) for anything when this happened. This is not the first time my car has unnecessarily automatically slowed down quickly but this is the first time it’s ever been this abrupt and severe. I will be taking my car to be inspected for this issue and if my neck and shoulder still hurt in the next day or two, I will also be going to the doctor about the incident.