I tend to worry a lot. Is this a sign that I have paranoia?

Paranoia is more than too much concern or worry; it tends to involve a more intense sense of doubt and mistrust. This is different from worry - which is more a feeling of anxiety, hesitation, nervousness and uneasiness without automatically thinking and/or believing that other people are trying to harm you. Most people who worry can tell fact from fiction and have a good sense of situation. On the other hand, paranoid psychosis is a phony, rigid belief that doesn't dislodge even when one is confronted with evidence that disproves the belief.

Is paranoia only associated with schizophrenia?

NO.  Paranoia is a symptom that can occur in several other mental disorders including bipolar I disorder. More than 50% of individuals with bipolar I disorder have psychotic symptoms -- delusions or hallucinations -- when they develop mania.

Paranoia though is most common in schizophrenia. One may see it in people who abuse illicit drugs like cocaine, LSD or methamphetamine.

There are also some people who have mild degrees of paranoia and tend to function well in life. These people have a paranoid personality but are not delusional.

There are many examples of paranoia in people who have suffered brain trauma. Paranoia is also common in hospital patients but in such cases the paranoia is only mild and rarely reaches the severe intensity seen in schizophrenia. People who have borderline personality do tend to have a certain paranoia and tend not to trust people. These people live on the fringe of neurosis and psychosis.

Can you please tell me if paranoia is the same thing as not trusting someone?

Well, paranoia is much more than that. Paranoia is an overstated and unsubstantiated sense of suspicious or mistrust of someone. During paranoia, you may develop false beliefs that someone or something is planning to harm you or has evil intentions toward you. If you cannot distinguish fact from fiction there you have an impairment in relative awareness. If you are absolutely persuaded that others are against you and you cannot figure out alternative explanations for how you feel, then your paranoia is delusional in nature and intensity.  In psychosis this is the major problem- people cannot tell what is real and what is fiction.