Minor unpleasant incident has left me triggered

Quick info - I have PTSD following a terrorist attack, I've had counseling and it really helped. It's many years ago and generally nowadays I don't get triggered often, although it does happen occasionally and with very specific noises or unexpected news items about the attack.

Earlier today I was involved in a very minor car shunt - a car backed into me. The person then driving refused to cooperate with insurance and got aggressive toward me.

Thankfully they didn't attack me, but I called the police who attended and sorted everything out (they're uninsured which is a pain, but their car got seized so karma!) It was all very low key, non dramatic and ultimately my car is insured for the repairs.

So why now, 5 hours later, am I wide awake and going over and over and feel shaky and unsettled. It's like I have zero capacity to deal with any kind of unexpected stress.

I need to go to sleep but I just can't settle enough.

Anyone have any similar experiences and or advice to help me get this non-trauma out of my brain/system? I'm so cross with myself that I'm reacting like this.

Thanks in advance.