Why was freaky nikki so freaky?

Just watched for the 26th time and noticed something new… why was freaky Nikki yelling and acting crazy more progressively throughout the movie? Why couldn't she just get over it and be normal like bear wanted her to be? (like when they had sex even though she seemed to be upset when they kissed)

Idk guys I think I should watch it 62 more times to get to the bottom of this

(Directly inspired by a post I just saw that I originally assumed was posted in here lol)