Mental illness cannot always be clearly differentiated from normal behaviour.

For example, distinguishing normal bereavement from depression may be difficult in people who have had a significant loss, such as the death of a spouse or child, because both involve sadness and a depressed mood.

In the same manner, deciding whether a diagnosis of anxiety disorder applies to people who are worried and stressed about work can be challenging because most people experience these feelings at some time.

The line between having certain personality traits and having a personality disorder can be blurry.

Thus, mental illness and mental health are best thought of as being on a continuum.

Any dividing line is usually based on the following:

• How severe the symptoms are;
• How long symptoms last; and
• How much symptoms affect the ability to function in daily life.