What is a characteristic symptom of a sleep disorder involving panic and intense fear?

The characteristic symptom of a sleep disorder that involves panic and intense fear is indeed sleep terrors. Sleep terrors, also known as night terrors, typically occur during deep non-REM sleep and are most commonly experienced in children, though they can also occur in adults.

During a sleep terror episode, the individual may suddenly sit up, scream or shout, exhibit signs of intense fear, and have an increased heart rate. They may not be fully aware of their surroundings and are often inconsolable during the episode. This intense fear and panic is a hallmark of sleep terrors and distinguishes them from other sleep-related phenomena.

In contrast, sleepwalking involves complex behaviors performed while in a state of partial arousal from sleep but does not typically feature the acute fear response characteristic of sleep terrors. Nightmares, while they do involve fear and distress, occur during REM sleep and are recalled upon waking. Insomnia refers to difficulty falling or staying asleep and does not involve episodes of panic or intense fear. Each of these conditions has different underlying mechanisms and presentations, with sleep terrors specifically associated with the manifestations of panic and fear during sleep.