What can years of isolation do to a human mind?

I recently am coming up on my 4 year anniversary of being complete alone, hardly leaving the house, home-schooled, at 17. So, since 14, I have been like this. I was in school originally, but left due to some incidents. I haven't seen a person my age IRL, for those 3 years. Not to mention another human being besides my parents. Sure, the occasional newsletter man, mailman, and stuff like that, but not a genuine interaction. I've had a lot of people tell me this is bad for me, and my health. I wanted to know if anyone else has gone through this and their experiences? I am very curious.