Sleeping afraid to turn off the light may not be a mental illness, but an overly nervous, fearful emotional problems, if serious, there may be anxiety disorders, phobias of mental illness. If it is relatively mild, it may be a kind of bad behavioral habits, that is, from childhood to sleep with the light on, it is possible that when you grow up, you do not dare to turn off the light, and you are already accustomed to sleeping with the light on, and once you turn off the light, on the contrary, it will destroy your own habits, so that you do not have the means to adapt. Because of the tension and anxiety, some people may have too low self-esteem, easily sensitive, less courageous, always dependent on others, less independent, sleep alone at night there is a possibility that they will be easily worried, easily nervous, and must sleep with the light on. Finally, more serious problems, such as anxiety, depression type of mental illness, easy to be nervous, afraid, it is possible that the night must turn on the light, otherwise it will fall into the tension, fear, anxiety, repression of emotional problems.