Not necessarily a Concussion, but a Whiplash Injury.
Whiplash effects from sudden braking( 65 miles/hour is a high risk factor)
in your case would be classified as an Acute Whiplash Injury.
Your injury is likely a grade 3, but regardless, it should be evaluated for the
severity of cervical injury(usually at C2,C6 or C7) and associated neurological symptoms.
When wearing a seatbelt with shoulder restraint, it helps prevent serious injury, but paradoxically the rates of whiplash are higher than without the shoulder restraint!
So please consider getting a medical evaluation, specially if symptoms persist or worsen.
There are other considerations, besides health implications, such as legal,
insurance and employment related issues, which might arise from this incident.