I've been a Castle Of Spirits fan for a very long time, and can't think of a better place to share this story.
It is completely true, and it freaked me out so badly that it stayed on my mind for days after it happened.

I work the night shift at JFK airport terminal 3. Two weeks ago I was working down by one of the gates and had to use the restroom. Now everyone has a "spot" as we all say, that they are comfortable in, because it's cleaner and less to never used by the public. But because my business could not wait any longer, I opted on going to the ladies room above the gate area by a Samuel Adams bar.
I've never been up there, and noticed as I went in that it was even cleaner, and warmer than my "spot" (at night the AC in the terminal reminds you of a winter day) so I decided this should be on my list of comfy places also.

While touching up my makeup a bit in the mirror before using the toilet, I heard a low moan as if someone was in pain, and it sounded as though it was coming from one of the stalls on the end. So, being the silly individual that I am, I start chuckling quietly to myself. Don't ask why, I just thought it was funny is all. So, I head to the first stall on my left; there's three on the left, three on the right when you walk in, and noticed all of them were wide open and empty. I was the only one in the bathroom!
Like I said before, I really had to go, so I put it out my mind. Thought maybe I was hearing things.

The moan got a little bit more louder now. I stood in the stall for a moment and thought of all the things that can make a noise like that, and I came up with old plumbing. I struggled with that for another moment because this noise sounded like a person in pain, not old pipes or bad plumbing, it was a human sound. And as I settled my mind to just go with the bad pipe answer, the moan got so loud that it now filled the entire bathroom to the point that I could not pinpoint the location from which it was coming from.

That was it for me, I didn't want to be in there another second and high tailed it out of there. But, I was still very desperate to relieve myself, and it would take five minutes to walk to another bathroom, five minutes I could NOT spare, and this one was right there...but I'm afraid to go back in! So, I sucked it up and went back in. Stood at the door for a minute, no sounds. Did my business super quick and as I'm washing my hands...the moaning starts up again, this time I nearly peeled out my skin because the sound was right next to my ear! Instead of flying out of there in horror, I got mad at being frightened so badly and let out a few choice words letting this spirit (yes I finally got that in there was haunted) know that I don't care what their problem was, but I hated them scaring me that way.
As I turned to storm out, I heard one long, low pitiful wail that made my skin crawl, then weeping. Because this weeping sound seemed as though it was coming towards me fast, I flung open the door and broke into a run. I ran half the steps that took me back down to the gates and jumped the rest (about 10). When I hit the bottom, my friend, a security guard looked up at me in concern. He rushed over wanting to know what happened, and when I was done telling him. He said that I was the sixth female that night to run out of that bathroom. Two passengers, a cleaning lady, the female security guard who he relieved, and a TSA federal officer.

That was my first and last time up there. I went home the next morning and the incident stayed on my mind to the point that I went to bed with it being the last thing ON MY MIND days after!