What would you do?! Help please.

Tonight at around 11pm, I was driving to work on complete dark, back roads, no cars ever pass and I had to stop to get something out of my bag. So I pulled over in a gate (still on the back road) I could see a car coming behind me to pass.. so I continued to get something out of my bag that was on the passenger seat. I remember thinking ‘where has that car gone?! I looked in the mirror and couldn’t see the car, I turned to my right and there was the car… stopped DEAD next to me, a man just staring at me, my heart sank. I looked at him and thought ‘what do I do? He’s blocked me in, hopefully he will go now… he continued to stare at me. I started to panic so I looked at him and mouthed ‘what’??? He didn’t respond and continued to be pulled up next to me completely starring for about two minutes, he then drove off so I drove off behind him trying to hopefully remember his number plate and then he pulled in again & stopped, I just kept driving my heart was beating so bad… my question is, what do you think he was doing ?! And shall I report it to the police??

Edit - yes I’m from the UK and secondly I wouldn’t have minded if he pulled next to me to check if I was ok, it was the fact he stayed in his car staring at me for over a minute, didn’t even bat an eye lid when I looked and him and said ‘yes?’ He didn’t wind his window down (if he thought I was not ok) I was parked in a lay-by in the middle of fields, backroads. No houses around for miles. I wasnt in an entrance to a property