Being unsociable can have various causes, ranging in severity from 'needs attention' to 'life-threatening'. Finding the true cause means ruling out or confirming each possibility – in other words, diagnosis.
Diagnosis is usually a complex process due to the sheer number of possible causes and related symptoms. In order to diagnose being unsociable, we could:
Sociability. By nature are you sociable or unsociable?
Possible responses:→ Unsocial/introverted
→ Average / don't know
→ A 'people person'/extroverted
The inability to collaborate with others and social isolation are possible symptoms of paranoid personality disorder.