The Head-Eater.

In a city where young people disappear, Anya goes through the process of losing her best friend, Mayra, after she transfers to another school. Anya's loneliness and sadness attract Orion, an alien who attaches to her head, but which no one else sees. He manipulates Anya's dreams to convince her to go to his planet, but she clings to her chaotic reality.