Is this weird or am I overreacting?

A few days ago I (17yro female) was wearing a sun dress that had a low neckline and a short skirt. Usually I cover up a lot. Although it wasn't as revealing as what some other girls wear , I was showing a lot more skin than I usually would. I had been getting compliments all day aboit how pretty and summery my dress was. I attend a sixth form that is part of my old high school. I was walking by myself down a hallway and the only other person around was this new male teacher - he'd been there a few months but we had never spoken. He was stood still in the hallway, and he was staring at me the entire time I was walking down the hallway, fixated on me for a good 10 seconds. It's not very often I get uncomfortable and I'm not one to start drama, but this made me feel really uncomfortable, so I tried looking down or turning my head away to avoid eye contact, but when I looked back he was still staring at me. No-one had ever looked at me like that before, he looked almost mesmerised / fixated on me. As he was stood in the middle of the hallway, when I got to where he was he gave a really awkward quick hi, but it didn't sound as casual as teachers usually do when they greet a student in the hallway, then he stepped aside and I said hi back and carried on quickly. I came back a few minutes later and he had gone. My gut feeling was that something was off. Was this weird or am I overthinking this?