Black Goo Puddle.

You’re sitting in your bed when you see a black goop puddle, you don’t realize it’s a parasite. Once you get near, touch, or are asleep, it goes inside of you and you become a large black, werewolf like creature with white glowing eyes and sharp teeth. You loose the ability to speak and it makes you aggressive, animal-like (meaning your basically an animal now) and it makes you attack humans.