Well, from a physiological perspective, I don't believe the term 'insane' is used to much anymore. More like 'imballanced'. Insanity is really a general purpose word, used to describe radical, behavioral abnormality. Now that we understand the biology of the brain better, we have terms for these disorders. Such names include OCD, Dissassociative personality disorder (multiple personalities), Bipolar Disorder (manic depressive), Schizophrenia (insane), and so on.
Most of these disorders are due to chemical imballances in the brain. The brain works off of chemical and electrical transmissions. When these transmissions are interfered with, or the method of the transmission is damaged, people display behaviors which we would consider 'insane'. Note that this isn't a perspective change. Most people with these disorders are more than likely born with them or possess genetic qualities that will predispose them to getting it later in life.
But what about shell shock and victims of abuse? We call that Post Traumatic Stress Disorder. While the above disorders are mainly genetic in nature, PTSD is caused by extreme trauma which can be found in extreme situations such as one's life being threatenned, torture, sexual abuse, etc. PTSD usually occurs when the person is not allowed to recuperate from the previous stress levels of the traumatic experience(s), thus keeping the vollume of certain chemicals at a constant level (which they should not be at) and altering brain chemistry. Again, not a perspective shift. This person has had this disorder forced on them.
And that's insanity in a nutshell, that is to say, insanity is more of a buzz word these days. That's not to say that people don't display aberrant behavior, but that we have a better idea as to what causes it.
Edit: Answering the actual question. There's a huge line between perspective shift and insanity. Changing your opinion about something is not a mild case of insanity. Changing your opinion to say, "I once thought the sky was blue because of light passing through the atmosphere, but now I know better. A group of hyper scientists created aerosol to change the color of the sky. They marketted it as a way to easily force chemicals from a can under pressure, but of course they didn't tell anyone their true motive. Even the texts have been changed, saying that the sky has always been blue. But I know better, it used to be purple" is something else entirely