Mental illness is a disease that causes mild to severe disturbances in thoughts and/ or behaviour, resulting in an inability to cope with life’s ordinary demands.  Some common mental disorders are- depression, bipolar disorder, dementia, schizophrenia, anxiety disorders, eating disorders, addictive behaviours.

It is a myth that mental disorders are rare and happen to someone else. Infact mental disorders are widespread and common. According to National mental health survey of India: every sixth Indian needs mental health help. All age groups are affected but is more common between 30 to 49 years and above 60 years of age.

Anyone can develop a mental illness.

It can be due to stressful event or a series of stressful events in life.
Genetic factors can also play a role in leading to mental illness. 
Biochemical disturbances in the brain also lead to a mental illness.
The above factors may associate together and can cause a mental illness. 

One should pay attention to the sudden changes in the thoughts and behaviour of a person. Some common symptoms which are seen in the mental illness are (they should not be due to recent substance abuse or any medical condition):-

Confused thinking
Prolonged sadness\ irritability
Feeling of extreme highs and lows
Excessive fears and worries
Social withdrawal
Dramatic changes in person’s sleeping/ eating habits
Increase anger
Strange thoughts {suspiciousness}
Seeing /hearing things that are not there
Growing inability to cope with daily activities of life
Suicidal thoughts
Numerous unexplained physical ailments
Substance abuse

Some symptoms that are common in older children and pre adolecents are:-

Substance abuse
Inability to cope with daily activities of life
Changes in the sleeping or eating patterns
Excessive complains of physical ailments
Changes in the ability to manage responsibility at home or at school
Intense fear
Increase anger 

Signs and symptoms of mental illness in younger children :-

Changes in school performance
Poor grades
Changes in the sleeping and eating habits
Excessive worries or anxiety ~like refusal to go to school or bed
Hyper activity
Persistent nightmares
Persistent disobedience or aggression
Frequent temper tantrums

On recognising a mental illness in someone, he or she must be encouraged to meet a Psychiatrist at the earliest. Most of the mental illnesses do not improve on their own and if left untreated it can worsen with time and can cause serious problems.

A friend or a family member is encouraged to accompany the patient to the Psychiatrist in initial few visits. The treatment differs from person to person. It can be in the form of medicines and/or talk therapy, lifestyle changes or the combination of all of the above.