Instantly diagnosing schizophrenia is somewhat possible but not a good idea. It is something you can read about the symptoms and have a good idea if you have it or not, but you could be right or you could be wrong. It is highly recommended that you go see a professional to let you know, through a formal diagnosis whether you do have it...or not.
When a person is suffering from Schizophrenia, they are not fully in touch with reality. That brings about a true problem when self diagnosing. A doctor will perform a number of tests before determining if a patient is or isn't suffering fromt the disorder so it is not likely that one will know instantly.