There are other mental illnesses than schizophrenia. Ever had to hang out with a total borderline? They are not insane per se, just that they kind of are, because nothing you say will freaking sink in.
Rrring!
"Have you forgotten about me?"
"No. I'm busy, I was going to call you later."
"OK............. Oh, you're just saying that."
"No, I am honest but I have to work now. Can I call you back in two hours?"
"You sound angry now, You're angry with me."
"No I'm not, but work is kind of stressing me out and I have to finish this, like right now!"
"So work is more important than me?"
"No, but this can't wait. I will call you back."
"Are you sure you're not mad at me?"
"Yes. Bye"
Click!
Rrrrring....
"You hung up too fast. I feel you didn't say bye properly."
"AAH! Please!"
"Why are you rude?"
"Pleasepleaseplease stop I have to work!"
"I didn't deserve you being rude to me. Maybe I did. I'm useless."
"NO! You're not useless, but I don't have TIME FOR THIS!"
"Now you're upset!"
"Sigh, yes, I am now. Thank you very much."
"I always fuck everything up, I'm so terrible.... Cryyyyy..."
Call it insanity if you wish. I actually do. Sure hallucinating and being followed beats this but this isn't sane either.