TSR is not a space for anyone to diagnose PTSD on in the few short lines you have typed. If you are genuinely worried seek professional medical advice.
If you have been half frightened to death your brain isn't going to let you forget it in a hurry. You will go over and over it again for many weeks, even months. If you have never experienced anything like this in a lifetime your brain will be very upset as the fear takes your brain's recording of 'fear', 'threat' to a whole new level. It will scale 11/10 on the frightening events scale. Gradually over time when you have carried on enough without anyone else attacking you your brain will let you relax again. So this is a very normal reaction to a frightening event.
Do not blame yourself - there are unfortunately some random people out there who need no winding up to find a face to fit their pent up anger. Blaming yourself is also an indication that you have been traumatised. It's ok to think like that, but only for a moment. In any life event where something nasty happens, you should review the event to see if you could have done something differently or better, in order to keep yourself safe. That is aim of survival. Those who have enough IQ to do this and then do something different next time to prevent and stay alive are the ones who survive. Review your own actions honestly but the behaviour (sand potential assault) by a random stranger is not your fault. What are the chances of this repeating? (choose your socialising area & your friends carefully) The behaviour that is threatening here is their behaviour, not yours. They are the ones who need to blame themselves but won't because their own internal brain is a damaged hardwire.
Re-evaluating the 'what ifs' in life is a normal way of processing the upset you experienced. Turn it on its head and ask yourself how many nights out and years you have been living without any similar events happening? Not all human beings are mad dogs. That is the context. Wrong place wrong time - an unfortunate random event but you survived to live to tell the tale.
If you need more info look at the NHS advice on PTSD - 'watching wait' approach.