The dark and peaceful quiet is instantly ripped open as his piercing scream fills the room. His eyes and mouth are wide-open and filled with unseen terror. He’s soaked to the bone with sweat and appears to be experiencing a horrible nightmare, but in the morning he’ll remember nothing of the event and claim to have had no dreams at all.

Night terrors (or sleep terrors) differ in subtle ways from their distant relative, nightmares, according to Dr. Freddie Wilson, a board-certified sleep specialist at Southeast Regional Sleep Disorders Center in Anderson, S.C.

“Nightmares occur during REM sleep, when people do most of their dreaming. It’s really a bad dream. You have to be in REM sleep to have a nightmare, and they’re usually remembered. You know that you were about to be attacked in your dream, and then you suddenly woke up,” Wilson said.

Night terrors, on the other hand, occur during non-REM sleep.

The person doesn’t remember it or remembers very little.

“They may look like a nightmare to the observer because the person is thrashing around, but he appears to be terrified. There might be blood-curdling screams, extreme fright, dilated pupils, sweating and rapid breathing,” Wilson said.

Night terrors are categorized as arousal disorders because sufferers are aroused from a certain stage of sleep, Wilson said (also in this group are sleepwalking and sleep-related eating). Sleep terrors and sleepwalking occur during the first third of the night, whereas nightmares in REM sleep occur during the last two-thirds of the night.

“During night terrors, the person is basically sort of awake. If the person were hooked up to an EEG, they would appear to be awake,” Wilson said.

Although most common in children between the ages of 3 and 12, and fairly uncommon after age 20, night terrors can occur in sleeping adults if the conditions are right.

“A lot of it depends on what you’re doing,” said Jeff Cotton, a clinic coordinator at AnMed Sleep Diagnostics in Anderson. “Sleepwalking and sleep-talking are related to a stressor such as a job, a marriage or family events.”

It’s certainly difficult, not to mention incredibly frightening, to just stand by and watch a loved one in the throes of a night terror, but waking him or her up is ill-advised.

“You just keep an eye on them and try to keep them from hurting themselves or anyone else,” Wilson said. “It’s an autonomic abnormality. They’re not thinking anything or dreaming anything. They’re not having any dream-like thoughts. They’re not acting out their dreams (that is an REM behavior disorder, which is a rare condition).”

The best thing for a bed partner to do, Cotton said, is to give the person ample space to prevent injury to either partner.

“While they’re having this, they are very much in a fight-or-flight mindset, and they very well could do damage to something or someone,” he said. “They really are at the mercy of those things, and quite honestly if you look at the artists’ rendering of (night terrors), they’re very frightening and hard to understand, and you get a big mythology built up around them.”

Unlike sleepwalking and sleep-talking, night terrors are likely related to sleep deprivation, Wilson said. One of the treatments is to make sure sufferers get enough sleep at night. Also, identifying stress triggers so one can avoid them and finding better ways to deal with stress often can bring relief.

Night terrors are considered mild if they occur less than once per month and no harm is done to the patient, moderate if they occur less than once per week without harm and severe if they occur almost nightly and the sufferer causes injury to himself or others.

If the night terrors continue for longer than three months, one should consider medical treatment.

“Basically, if it’s something that happens more than once or twice a week or if you’re a danger to yourself or others,” Cotton said. “… Sometimes we’ll have a spouse come in with bruises or a black eye, and he or she is leading the patient by the hand.”