Don't try this at home! Diagnosing a mental illness takes training and experience. You can assess your symptoms and come up with a good hypothesis as to what's wrong, but mental health professionals spend years learning the nuances of mental illness so that they can differentiate between different types of mental illness.

One of the first things a mental health professional will do to help find a diagnosis is make sure that you are physically healthy. This is because many physical conditions can mimic mental illness. One common example is elderly people with mental status changes. Mental status simply means the state of your mind. There are over a dozen criteria used to determine your mental status. The mental health professional will conduct an interview with you to help assess these criteria. But for the elderly, common ailments such as a urinary tract infection, low or high blood sugar or low nutrient levels can cause mental status changes that make others think the person is mentally ill.

Next, an interview is conducted where the professional will ask questions about your history and current symptoms. They will ask questions about your family history as far back as you know. They'll want to know if anyone in your family has mental illness or emotional problems because some mental health issues have a genetic component. They'll ask if you've ever used drugs or alcohol. While they are interviewing you they will also be watching for symptoms you may not be aware of. They'll ask about your education and what kind of work you have done in the past, and what you are doing now. Sometimes the interview can't be completed in one visit, and the professional will ask you to come for a return visit.

Once the assessment process is completed, the professional often will write a report detailing their findings. You may have to request this report as it isn't always automatically given to you. You should ask as many questions as you can so that you understand the daignosis. Believe it or not, there is a diagnosis called "no diagnosis." The official list of psychiatric diagnoses is found in a book called the Diagnostic and Statistical Manual of Mental Disorders. The professional will consult this manual to match your symptoms with a diagnosis. You won't always see them open the book because some of us have been doing this so long we carry the information in our heads! 

Some mental health issues take a while to diagnose. Sometimes the diagnosis requires psychological testing, or even a period of observation in a hospital. In any case, the more thorough the evaluation, the more you can be sure that the diagnosis is accurate. 

As a crisis clinician I have seen many conditions mimic mental illness. I saw a man in the emergency department who complained of a sudden onset of depression and anxiety. Within six months he had lost a successful business and deteriorated in functioning so that he was not eating well and not taking care of his daily needs. He had no history at all of mental illness or emotional problems. He came to the emergency department because he had been having thoughts of suicide and that scared him.

When I interviewed him, I learned that the man had had a sudden onset of headaches that coincided with the change in his mental status. He was taking a lot of over the counter pain medication with no relief. I asked the doctor who was caring for him to check the man's medical condition related to the headaches, and they did a head CT. This is a special kind of x-ray of the brain. They discovered that the man had a mass on his brain and he was admitted to a medical unit instead of a psychiatric unit. He was not referred to the crisis service again.

Another client was confused and anxious and was sent to the emergency room by her primary care doctor, who requested that she be placed on a psychiatric unit. In this case she first was seen by the emergency room doctor, who found that she had hyponatremia - a conditon where there is too little salt in the blood. She too was admitted to a medical unit as her condition required medical intervention. After she was treated she was able to return home without the need for psychiatric intervention.

Another common example is substance abuse withdrawal. I saw a woman who was depressed and anxious, yet she seemed to have no previous mental health treatment history. As the interview continued I learned that she used alcohol daily, cocaine a few times a week, and marijuana daily. Yet when I asked when was the last time she had used these substances, she reported two to three days ago. I realized that he symptoms could be cause by withdrawal from these substances. I called the local detoxification center, where a substance abuse counselor confirmed my suspicions. Alcohol withdrawal is often accompanied by anxiety, while discontinuing the use of cocaine can cause depression. The client agreed to go into a substance abuse program and they agreed that she was a good fit.