Congrats, you're not psychotic.
Treatment is pretty much the same though, antipsychotics.
Yes, or else I could walk in and be like "Yo, I have anxiety, hit me up with some roofies." and the dr. would be like, "OK, your not a professional, but I don't need to diagnose you so here is your drugs."
prescribing meds to you without an accurate diagnosis and hearing your symptoms and feelings, would be unprofessional as well as unethical. in order to be prescribed anything, a doctor must look at all aspects of your health, physical and mental, and make a definitive conclusion what, if any, medicine, would alleviate your symptoms and cause you to function better on a daily basis.
Yes, there must be diagnosis before treatment. Actually it's a rare thing when doctors treat first before having a diagnosis, though I think it can happen with complicated diseases.