Clinically, it is customary to classify diseases into two categories: organic diseases and functional diseases. Functional diseases are characterized by: clinical symptoms, some of which are not mild; variable and sometimes severe; many complaints, patient suffering, and unsatisfactory drug therapy; many psychological problems such as anxiety, fear, and suspicion; pathological changes in the corresponding organs that cannot be detected by repeated physical and laboratory examinations; patients’ quality of life and work efficiency are affected, but their healthy life span is not threatened. Functional disease is a disease in which only organ function is dysfunctional without pathological changes in organ morphology and structure. The diagnosis is usually made only after a series of examinations and a certain period of observation to exclude organic diseases. Common functional diseases are: 1. Functional hypothermia: Some people have fluctuations in body temperature between 37.4℃ and 38℃, and the cause of hypothermia cannot be detected by repeated observation and examination. The patient has good energy and physical strength, and may have hypothermia due to phytonadic dysfunction. It is mostly seen in women aged 20 to 40 years old, and pediatric summer fever also belongs to the range of functional fever. 2.Functional hypoglycemia: A few people have unexplained hypoglycemia, which may be related to gastrointestinal dysfunction and vagus nerve excitation. Due to the sudden entry of food into the intestinal tract, certain intestinal polypeptide hormones are produced while glucose is rapidly absorbed, and the latter strengthens the effect of glucose excitation of pancreatic islet cells. It is commonly seen after gastrointestinal anastomosis, after labor and after starvation, and is also called functional hypoglycemia. 3, vasovagal syncope: especially in young women. Syncope is mostly induced by emotional excitement, fear, anxiety, pain and so on. Usually there is a loss of consciousness lasting from a few seconds to a few minutes. There may be a mild decrease in blood pressure and slowed heart rate at the time. There are no cardiovascular or cerebrovascular lesions on multiple examinations for multiple episodes. 4.Functional headache: common in neurasthenia, many people have depression. There is no certain regularity of pain, with the feeling of heavy pressure at the top of the skull and tightness around the head as common complaints. The headache is accompanied by insomnia, memory loss and mental inability to concentrate. It is also called tension headache, psychogenic headache or neurological headache. 5.Functional palpitations: palpitations and chest tightness are common in young women, and the symptoms appear mostly in the quiet state, but reduce or disappear when working or exercising. There are no abnormalities on auscultation and electrocardiogram or occasional premature beats. There are very few patients with episodic supraventricular tachycardia and atrial fibrillation without organic lesions, which may also be the cause of functional palpitations. 6, functional shortness of breath: some patients complain of shortness of breath, shortness of breath, poor inspiration, a sense of “not enough air”, as deep inspiration, oxygen can not significantly relieve the symptoms, systemic organs can not detect pathological changes. It may be caused by insomnia, negative emotions, disruption of life rhythm and other factors. 7. Functional liver pain: Some patients who have suffered from hepatitis B still have vague pain in the liver area from time to time after hepatitis is cured, especially when they are depressed and when hepatitis B reoccurs. After a detailed process, no organic lesion is found, which may be due to the fear of hepatitis B. 8, functional dyspepsia (FD): some data show that the prevalence of the population of about 20%, manifested as fullness after meals, nausea, belching, vomiting. Endoscopic examination without upper gastrointestinal tract and systemic diseases. Also known as non-ulcer dyspepsia. 9, functional vomiting: also known as psychogenic vomiting, more family history, different from functional dyspepsia, mostly a single vomiting symptoms, may occur for no reason, more when eating, the onset and cessation of vomiting are faster. 10, functional abdominal pain and diarrhea: irritable bowel syndrome is often a single abdominal pain, diarrhea or both alternately. Abdominal pain and diarrhea are often stubborn, the duration of the disease is also long, the drug treatment is not ideal, but after and good prognosis, no organic lesion cause. 11, functional urinary frequency: some hypersensitive people, either at night when it is difficult to sleep, or during the day when emotional tension, frequent urination, urine volume is generally not much. There is no abnormality in urine, urinary tract and prostate examination. The symptoms can be reduced by shifting attention. 12, benign recurrent hematuria: plain examination mostly has microscopic persistent hematuria, which may be more likely to appear after strenuous exercise. Although the hematuria is still present after several decades, the kidney function is not impaired, and many tests are unable to detect the cause, and there is no obvious impact on health. 13.Functional edema: It is mostly seen in fat women of childbearing age between 20 and 50 years old, with periodic characteristics. There is no organic lesion of heart, liver or kidney, no abnormal serum protein, no venous or lymphatic obstruction, no hypothyroidism or cortisolism. Patients are often anxious because the cause of mild swelling cannot be identified. 14, functional joint pain: often presents with indeterminate multiple joints with mild pain. The history is long, but not progressive aggravation, no abnormal local signs, no restriction of activity, and may be accompanied by other neurological disorders. Attention should be paid to exclude hypertrophic, rheumatic and other organic arthropathy. 15.Functional growing pains: Growing pains are not a disease, but a transient leg pain without clear pathological changes, and the causes of such symptoms are all related to the growth after preschool. During this period, children grow fast and their activities increase greatly, but the development of muscles and bones and the functional cooperation between them are not yet perfect, so that the muscles of various parts are subjected to uneven forces, so that muscle fatigue pain or ligament pulling pain occurs at night after quiet. Growing pains are a temporary phenomenon in the process of growth and development of children, and can be self-healing as children grow up and mature.