Why I'm afraid of the dark

Pretty much when i  was a kid me and my siblings played this game every time my parents were gonna be out of the house at night for a long time. Normally it would be when we have guest stay with us. It was like hide and seek in the dark only one person would hide. The rest would run around searching and when you found the person you would hide with them until everyone found them. The last person to find the group would be next to hide. Well one night as we're playing this game (which i absolutely loved!!!) someone decided to hide in my sister Lisa's bathroom. I was about 9 to 11 years old I think. I remember following someone around and i turned my back for a second and when i looked back they were gone! I went to Lisa bathroom but it was too dark to see inside and i knew i wasn't allowed to turn the lights on. This fear came over me and I just knew someone was in there starring at me. I didn't want to go into the bathroom to find out if they were in there. I think i even said something to the effect of "i know you're in there". But because they never answered that fear never went away. And yes i was so scared I peed my pants. So I quit playing hide and seek in the dark and was mad at the whole group of teens that were hiding. That is why I'm afraid of the dark. You never know whats hiding in it and it makes me pee my pants! Night light for life LOL!!!