I had a frightening experience today in my Y11 lesson and I'm not sure what to do...

A male student was standing chatting to a girl in the class, starter activity had been set and I asked him to sit down in his place across the room. He came right up to me, in my personal space and said "No!" I repeated the request and he shouted at me "What?! You haven't even started yet!" and I pointed to the board and said "that's the starter, you need to be doing it" He answered back again, something about me always having a go at him, but sat down. I felt so shaken up I emailed my HoD and Faculty Lead for help. The latter came and took the boy out and I got on with the lesson. The whole thing frightened me and my instinct was to flee and cry - I did neither.

It is difficult to convey tone but that and his body language were incredibly intimidating. I've followed the discipline procedure (we have an online 'concerns' system and it is recorded there) but I've been jittery all afternoon and still am. I feel like I can't face that student or in fact that class.

Am I being ridiculously dramatic? Or should I pursue it with the relevant senior staff? 

Should add I have nearly 18 years experience of secondary school teaching, most of it in this school.