Please help... I might be developing schizophrenia.?!

I worry about this sometimes. Whenever im in my psychology class and we're discussing mental illnesses, I get a little anxious. I just really dont want to have any mental disorders. My friend has serious personality and identity disorders, and has been smoking weed for awhile. He did meth about a month ago, and has been really showing signs of schizophrenia, such as delusions and extremely changed behavior and thought patterns. It scares the sh*t out of me seeing that happen to someone so close to me, and reinforces my desire to avoid having any mental illness like his.

I dont have hallucinations, i dont hear voices, and im pretty sure im not having a delusional view and thought patterns, which are the most common signs of schizophrenia. the only thing that makes me scared and sometimes makes my heart race when thinking about it is a self fulfilling prophecy type situation. ill try to give a little insight on how it goes on in my head:

I think to myself, "i dont have schizophrenia," but then i reconsider that thought with, "well if i did have schizophrenia, i wouldnt even know it," then its just a lot of anxiety and me trying to determine if it really is possible that i have/am developing schizophrenia, and then ill stop myself from all the thinking about it and think "Wait, maybe i do have schizophrenia or some kind of disease or i wouldnt be getting all anxious over absolutely nothing"
and the cycle continues.

Ive always done this; tryed to think of complex ideas that have unanswerable ends. Im intregued by psychology and the brains complexity and i cant help but try and find ways to create ideas and whatever that mess with my head. now that i read that all this over, i think i just need to stop watching movies like shutter island and inception... haha

but yeah any insight to what this might be, whether its normal and i just need to stop worrying and move on, or that i just have a little anxiety problem, or if i am in an early state of schizophrenia would be nice.

-one more thing; the first time my friend showed signs of having schizophrenia(he was changing topics every 10 seconds, was completely lost, and had drastic mood swings) was when we smoked some mary jane at my house. He freaked me out horribly and i had the worst trip of my life. I felt absolutely paranoid, my heart was racing, and i felt trapped. The next day, when i was sober and no longer feeling the effects, i was thinking about what happened to him last night, and i had my first self fulfilling prophecy about it which included me thinking that that could happen to me, and that i wouldnt even know it was happening, because he sure as heck didnt. i had a bad anxiety attack, had to sit down and try so hard to calm myself down and get off of that thought process. This was the first time i had a big problem with thinking i had schizophrenia and scaring myself. the thoughts went away for awhile, but whenever we discuss it in class, or we talk about my friend, the thoughts about having schizs come back and haunt/annoy me.

Okay, last little detail- Sometimes while having a conversation with someone, Ill mess with myself just to do it and start thinking fastly about having schizophrenia, and ill lose my train of thought and just be like "F**k..."


This whole thing just seems like a big mind trip that goes away after a day or two.