Paranoia (noun)

1. A mental disorder characterized by a persistent and excessive fear or suspicion of others.
2. An excessive or irrational fear or distrust of others.

Origin:

From the greek word "paranoia" meaning "madness" or "frenzy".

Examples:

1. He was suffering from paranoia and thought that everyone was against him.
2. She had a paranoia that someone was following her.
3. The patient"s paranoia was so severe that he couldn"t trust anyone.
4. His paranoia prevented him from forming close relationships.
5. The government's paranoia about foreign spies led to widespread surveillance.