Syncope describes fainting with a loss of consciousness. You can also call it blacking out or passing out. Some people experience warning signs and symptoms before they faint. For others, syncope can occur quite suddenly, without warning.

About one third of all people are likely to experience at least one episode of syncope in their lifetime. Many have one episode, and they tolerate it well. Others experience syncope many times and may become injured. This may be a sign of a more serious problem.

Syncope has many causes, and it’s sometimes hard to diagnose. The first step is diagnosis.