The last time I write a ghost story in this site, I was about 14 years old. I must admit, I am quite embarrassed by my previous writing, as at the time I didn't have the level of self-awareness that I had now. I hope this writing's quality has improved from the previous one.
As the title says, this isn't actually one of my experiences, but rather my grandma's. It happened somewhere during the 1930's, when my grandma was young and lived with my great-grandparents. My great-grandparent's house is very big, as they are a minor noble in the area.
One night, my grandma and her sisters (8 in total) are going to the bathroom. It was located in the back of the house, and to get there you must go through the kitchen. When they arrived at the toilet's door however, they saw a giant black figure standing with a fiery red eye standing in front of the door. Everyone run, except for my grandma, who for some reason can't see the entity right in front of her.
When her sisters told my great-grandfather, he had assumed they were just looking for an excuse to not go to the toilet by themselves, so he came to saw the entity... And immediately ran upon seeing it. Before my great-grandfather came however, my grandmother had decided to go straight to the toilet, and the entity suddenly slapped here across the face, knocking her out. That's when my great-grandfather came, and quickly grabbed her before fleeing.
For the rest of the night, none of my family members sleep well, and they huddle in the living room, fearing the possibility that the entity might come. Finally, when morning comes, my great-grandfather decided to check the toilet and to his relief the entity was gone.
To this day, not one member of my family ever figured out what that thing was, though some, like one of my grandma's sisters, was followed by an unknown thing until her death.
That is my grandmother's experience. I tried to preserve every detail of the story, but it was an old story, and my grandma had passes away in 2009, so I apologize for any mistakes in the story.
Your story reminded me a lot of this story by CallMeD: "My Biggest Regret" -