I have been reading some scary and kind of similar experiences about the unknown here in your ghost stories website. So I decided to share my own personal experience that happened when I was still in college.
I am now leaving here in California and my weird experience happened when I was 3rd year college at the Lyceum of the Philippines in Manila. I usually come in a little earlier before my first class and go straight to the library to read or review if I have a test or graded recitation in any of my subjects.
One afternoon (I took evening classes when I was in 3rd year since mostly my major subjects was on nighttime (on my way to the library, I feel an urgency to use the restroom. I was already in the 3rd floor since the library was located there, I stopped by and go to the nearest restroom. Unfortunately when I got there it was packed since the classes was just over, so I decided to go to the other end restroom which to my surprise was empty. I seldom used the restroom on the 3rd floor since mostly my classes were downstairs on the second or first floor.
I go straight to the first cubicle and did my business. When I'm done as I was washing my hand and looking at the mirror, another student passed by behind me and go straight to the last cubicle. I even heard the latched when she closed the door. I did not feel anything weird and as I was drying my hand two more students come in and they were even laughing and talking loud. To my surprise one of them go straight to the last cubicle which, still surprised me more, wasn't locked! I feel goosebumps and wonder, I just saw someone goes in there not too long ago.
I was trying to gather my wit's and was about to say something when the other girl asked me if I'm okay. I don't know what to say or how I'm going to answer her question and I don't want to scared them, but all I know at that moment was I feel weird and scared and cold. I just try to smile at her and said I'm okay and left the restroom right away.
I shared my experience to some of my close friends and classmate and they believed in me and even try to used that restroom which I dreaded not to used again. Until now I'm still thinking about it and what I experienced.