Mary Ann Hodes’ 3-year-old son has never been a great sleeper. And, like a lot of moms in that situation, she occasionally hears a whimper from his bedroom and wonders, “Do I go in?”

But when the preschooler started having sleep terrors, there was no doubt about whether to respond.

“It was screaming,” says Hodes, of Rodgers Forge. “It’s not even crying. It’s a horrible shriek. His eyes were open, but it was freaky, he couldn’t see me.”

When he woke up, Hodes says, it was as if nothing happened. “He said something like ‘Oh, hi mom.’”

“It’s extremely disturbing to us,” says Hodes, a graphic designer at St. Joseph Medical Center, “(but) he doesn’t seem any worse for the wear.”

The aptly named disorder is terrifying to everyone but the child experiencing it, medical experts say. And sleep terrors aren’t an indication that the child has any emotional problem or even a particularly troubling fear.

For the child, it’s actually a benign condition that begins as a toddler or in preschool and is usually outgrown by the age of 7 or 8, says Dr. Janet C. Lam, who has joint appointments in the Pediatric Neurology Department and the Sleep Center at the University of Maryland Medical Center.

Unlike nightmares, from which the child awakens and often can recall, sleep terrors are more like sleepwalking, according to Dr. Robert Meny, a pediatric sleep specialist at St. Joseph Medical Center and Franklin Square Hospital.

“Both are partial arousals,” says Meny. “The child isn’t awake. But it’s not a dream, which is what a nightmare is.”

For the parent, Meny says, “It’s very scary. You hear this unearthly scream. The parents run into their 4-year-old’s room. The child’s pupils are dilated, they’re sweating, their heart rate is racing.”

There’s no clear cause for night terrors. A December 2008 study in Pediatrics, the journal of the American Academy of Pediatrics, supports a genetic link for sleep terrors. If a parent had them as a child, there’s an increased likelihood that the child will, and if one child has them, there’s a good chance that siblings will.

Children who frequently experience night terrors may be tested for other sleep disorders, such as sleep apnea, which may trigger them.

Doctors also say that a child who has become overtired is more vulnerable to an episode.

“Sometimes moving up bedtime by just 30 minutes helps,” says Lam.

To treat persistent sleep terrors, doctors sometimes prescribe a mild sedative to break the cycle of partial awakenings, says Lam. Other times, doctors may suggest that parents time when the sleep terrors occur and try waking the child before the terrors typically begin.

Age eventually cures the disorder. By 7 or 8, few children experience sleep terrors, though they may sleepwalk as teenagers or adults, experts say.

Lynn Heiderman’s daughter began experiencing sleep terrors when she was 4 or 5 and suddenly stopped having them about a year later.

“It was very unnerving,” says Heiderman, a nurse from White Marsh. “A few times she’d run down the hall, down the stairs yelling, ‘No, no, leave me alone. Don’t touch me.’ The windows were open. I’d say, ‘My god, what do the neighbors think?’”

Other times, she’d yell about someone throwing arrows. Once, she seemed to think she was being held upside down.

She was never conscious during these episodes, and each time, Heiderman and her husband would hold their daughter. She felt rigid, and when it was over, she’d go limp. The terror lasted five or 10 minutes. But to Heiderman, “It seemed like forever.”

Heiderman’s daughter is now in her 20s. But the episodes made a lasting impression on her parents. “They are so scary,” says Heiderman.

It’s hard for a parent to shake, Hodes says.

“I was reading somewhere if the child remembers it, it’s a nightmare,” says Hodes. “If the parent remembers it, it’s a sleep terror.”

What are sleep terrors?

A benign disorder where the child is agitated but cannot be awakened or comforted. The child may sit up or run helplessly around, possibly screaming or talking wildly, and will not realize you are there even though his or her eyes are wide open.

It affects 2 to 5 percent of children ages 1 to 8. They rarely occur in adults.

When do they occur?

Usually within four hours of bedtime. It usually lasts 10 to 30 minutes.

What is the difference between sleep terrors and nightmares?

A child with sleep terrors partially wakes up and screams loudly or cries. He does not respond to attempts to comfort him, but will eventually settle back to sleep, unlike nightmares where a child responds well to parents’ comforting.

Why do they happen?

Genetics play a role. Psychological stress is not generally a problem, but becoming overtired may trigger sleep terrors.

How should you respond to them?

Stay calm. The goal is to help your child go from agitated sleep to peaceful sleep. Don’t try to awaken your child. Make soothing comments such as “You’re alright. I’m here.” Hold your child’s hand or hug them if he or she doesn’t pull away.

Keep the child safe, away from stairs, windows and other dangers.

You should mention the episodes to your child’s pediatrician. The doctor may want to evaluate for sleep apnea or other sleeping disorders. A mild sedative may be prescribed. If the terrors are frequent and the child is over 6, the doctor or sleep specialist may recommend waking your child before the sleep terror typically begins.

Sources: Dr. Robert Meny, pediatric sleep specialist at St. Joseph Medical Center and Franklin Square Hospital; Dr. Janet Lam, University of Maryland Medical Center; American Academy of Pediatrics; University of Michigan Health System