The Doppleganger

This happened when I was about 10 and my sister was probably 6. I had fallen asleep in my basement, and when I woke up, my sister was curled next to me. I was still scared of the dark at that time and my basement is really creepy, tried to shake my sister awake so we could sleep together upstairs, but she wouldn’t wake up. I eventually gave up and went upstairs. I was about to crawl into bed with my parents, when I noticed something was wrong. Because, curled up between them, was my little sister. I froze and just stared at them for several minutes, then walked to my room and locked the door. Even now that I’m older I still cant figure out what happened. There is no possible way for her to have gotten up there before me. And both of the times I clearly saw her face. This is the reason I firmly believe in doppelgangers.