Failure to function adequately
A person may cross the line between normal and abnormal at the point when they can no longer cope with the demands of everyday life and fail to function adequately, for example when they can no longer maintain basic nutrition and hygiene or hold down a job or maintain relationships.
David Rosenhan and Martin Seligman (1989) proposed some signs that can be used to determine when someone is not coping:
When a person no longer conforms to standard interpersonal rules, for example maintaing eye contact and respecting personal space
When a person experiences severe personal distress
When a person's behaviour becomes irrational or dangerous to themselves…