Many people experience paranoia to varying extents. Some describe themselves as paranoid when they feel very self-conscious, others when for instance they are walking around and a group of people nearby start laughing.
For others, it is considered to be more serious.
They may believe that the CIA or FBI or MI5 are monitoring them, or are trying to kill them. Others believe that these organisations are trying to make them kill themselves, or make others around them kill them.
Some people believe that people are trying to poison them, others that their telephone is being tapped, in fact there are so many variations on these themes that it would be impossible to list them all.
There is an email list / discussion board set up for people who are paranoid, and for those who support them or who just want to know more. To find out more about this group, go to Paranoia Support and to join, send a blank email to ParanoiaSupport-subscribe@yahoogroups.com