Funny story but how does it happen?

Oh man, I had a hallucination too one time, scariest thing ever. I bought Animal Crossing and was so psyched to play it on my gamecube. I only got to play it a little bit for that day because my cousin bought Mario Tennis. The next morning I woke up early and booted up Animal Crossing and started playing. I then saw my dogs paws on the windows trying to climb up, I thought to myself, ehh he can do it... then I thought it was construction people. A few minutes later I saw this alien looking thing at the window just staring at me. I jumped and ran downstairs and that thing jumped and flew away... I so freaking scared. I think things that cause hallucinations are drowsiness, hence the fact that I woke up early just to play Anima Crossing... I was scared going to my grandma's house ever since, but now I'm not.