My boyfriend told me that he's waking up in the middle of the night with a very weird feeling. He says that he feels his body is very heavy that he can't move, he could only move his eyes, and when he wants to move, he just cant, and it does happens to him alot. He didn't have a very happy past, and im wondering if this is a red flag of mental illness? Im very worried about him. What could this be? Why does it only happen at night?