The NAMI web site has a good article on common signs of mental illness in adults and adolescents. They can include the following:
- Excessive worrying or fear
- Feeling excessively sad or low
- Confused thinking or problems concentrating and learning
- Extreme mood changes, including uncontrollable “highs” or feelings of euphoria
- Prolonged or strong feelings of irritability or anger
- Avoiding friends and social activities
- Difficulties understanding or relating to other people
- Changes in sleeping habits or feeling tired and low energy
- Changes in eating habits such as increased hunger or lack of appetite
- Changes in sex drive
- Difficulty perceiving reality (delusions or hallucinations, in which a person experiences and senses things that don't exist in objective reality)
- Inability to perceive changes in one’s own feelings, behavior or personality (”lack of insight” or anosognosia)
- Abuse of substances like alcohol or drugs
- Multiple physical ailments without obvious causes (such as headaches, stomach aches, vague and ongoing “aches and pains”)
- Thinking about suicide
- Inability to carry out daily activities or handle daily problems and stress
- An intense fear of weight gain or concern with appearance
The article goes on to talk about how to get help, starting with the NAMI HelpLine.