So my sister has been acting really weird lately(past couple months), for example she often talks and laughs to herself a lot and it's not a happy laugh either, it's a weird lazy laugh. Ive asked her multiple times why she is laughing and she just shrugs it off and makes an excuse. I recently got a glimpse through her diary where she talked about how remembering about her ex(she had a bad breakup a couple of years ago with him) makes her feel "schizo" and that she enters this mode. 
I'm very worried about her now. Everyone around us is starting to notice her strange behaviour but no one talks about it openly. I've told my father about all this and we are trying to process how to respond to this. Any suggestions will be highly welcome since this is an urgent issue.
Any medical professionals here who can enlighten me as to what kind of a symptom this is and what to expect in the future? She is cutoff from her friends and barely talks to us(family) too. I'm really worried