Ghost in The Elevator

This happened a couple of months ago. I just randomly thought about it and decided to post it on here since I just discovered this site. It's a fairly short story.

I work night shift at a hospital. Due to the nature of my work I'm constantly moving between the three floors for this or that. I feel like I spend a third of my shift riding the elevators.

We have two sets of elevators, a set in the main lobby for visitors and a set for employees only. This happened on the first floor coming off of the employee elevators.

Right across from those elevators is a small, circular sitting area with tall windows looking out into a courtyard. I was alone on the way down from the second floor and as I stepped off of the elevator looking directly at the sitting area, I thought I saw someone sitting in one of the chairs until I noticed the light reflecting off of the glass of the window in front of them. I then thought I was looking through into a patient's room window, but that didn't make any sense either because there wasn't any rooms on that side. That's when I realized the figure was behind my reflection, as in, behind me, in the elevator.

They were crouched down, not sitting, behind the section of the elevator where the button panel was. They looked like a male teenager, roughly 17-18 years old with short, blond hair and wearing blue jeans. I can't remember what kind of shirt they were wearing but in the brief view I got before the elevator door closed, I noticed he was smiling at me for some reason. The whole encounter lasted about 3 seconds but felt so much longer.