Continuing from an experience I had...

The distance between me and that person kept getting closer. At first, I thought it was just a shape, but... I could tell it was a person, a man, by his clothes. What kept bothering me though was his head, or rather, his face kept turning black and then bright again. It was like he was looking up at the streetlight from underneath it... My legs kept moving, bringing us closer and closer. I was terrified but had to pass by, so I turned off my MP3 and gripped my umbrella tightly. If it was something strange or a person, I was ready to swing it. After about ten steps, I finally felt relieved. It wasn't something strange, it was just a person. He was just twitching his head like someone with a tic disorder. Still, I didn't loosen my grip on the umbrella, just in case. Luckily, I kept looking straight ahead, and he didn't seem to pay any attention to me... Phew, I thought I was safe... but then, the thought suddenly struck me, 'Why is that person even there?' The thought popped into my head. But I absolutely did not look back and just kept walking forward. I was really, really scared... What do you think it was?