I would like to share a story with you.
Back when I was seven years old, I used to have a re-occuring "encounter" with a person I just call "stranger" now.
It had continued for a few months, but then stopped all of a sudden.
You're probably thinking something like "Get to the story already god dammit!" So that's what I'll do now.
It all started on a fall, if I remember right. I had always had sleep problems, and I would lay in my bed for several hours before actually passing out. This happened at one fo such sleepless nights.
As I was laying on my bed, doing nothing, I heard footsteps. Of course I did not live alone back then, and disregarded it at first, thinking it was my mother having similar problems (my father was travelling, and I don't have siblings.) The footsteps got closer, and louder. By now it seemed like somebody... Heavy was moving. I heard the door open, and so I gazed upon who I thought was my mother.
As you have expected, this was not my parent. It was a stranger. A tall man with wide shoulders, holding a briefcase in his left hand. Needless to say, I was horrified. I covered myself in blankets and surprisingly passed out soon after. When I woke up, the man was nowhere to be seen (he would not stand there for the whole night, right?). I would ask my mother about the man later, to what she would hessitate, and say that it was just a nightmare.
I would run into the same man a couple of days later. Not at a night although. In fact, I was heading to school. He was standing there, at a bus stop. A gut feeling told me it was the same man... Same body build, carrying the same brief case. Now I managed to figure out their facial features - they looked middle-aged, had white hair and a large, strong-looking chin. He would then proceed to lock his gaze on me, watching. It was pretty creepy actually, and I tried not to look back at them. The man did not follow me on the bus.
The encounters continued, and I have stopped trying to let my mother know of the incidents (and I did not have many friends to talk about the man to either). The man would show up at many places - at a row in front of a store, on a bench in a park, in streets... Just, staring. That was all he did. And what would a seven year old do? I simply learned to deal with it, until the man just disappeared from my life one day, around February. I have never seen the man since. I had a few dreams (mostly nightmares) of him, though.
Now here's the question; would you think it would be possible for a person to experience hallucinations without any clear reason? Sleep deprivation perhaps? Or is it just a stalker in a fancy suit?