Signs and symptoms of mental illness can vary, depending on the disorder, circumstances and other factors. Mental illness symptoms can affect emotions, thoughts and behaviors. Examples of signs and symptoms include: 
Feeling sad or down
Confused thinking or reduced ability to concentrate
Excessive fears or worries, or extreme feelings of guilt
Extreme mood changes of highs and lows
Withdrawal from friends and activities
Significant tiredness, low energy or problems sleeping
Detachment from reality (delusions), paranoia or hallucinations
Inability to cope with daily problems or stress
Trouble understanding and relating to situations and to people
Problems with alcohol or drug use
Major changes in eating habits
Sex drive changes
Excessive anger, hostility or violence
Suicidal thinking
 Sometimes symptoms of a mental health disorder appear as physical problems, such as stomach pain, back pain, headaches, or other unexplained aches and pains.