What if that's not possible?

Many mental illnesses are difficult to diagnose. Even experienced doctors sometimes cannot immediately understand what they are dealing with, and insist on conducting additional tests on the patient who comes to the clinic for help. And you say it's easy, that it can be understood immediately if you have a mental disorder. But they may not show up, read about it at https://fherehab.com/learning/what-is-a-psychotic-break/. There are many signs of mental disorders and illnesses. The same disorder can manifest itself differently in different people, which is due to the peculiarities of the psyche and physiology. And if you don't have people close to you, it can be impossible to notice any changes in yourself.