If your child pierces the night with a blood-curdling scream when she’s sleeping—like my 6-year-old daughter did recently—she’s having a night terror, a common childhood phenomenon. Not to worry. Although night terrors can be a sign of something more serious, they’re typically harmless. Here’s what you need to know about what triggers night terrors, how they differ from nightmares, and what you can do to prevent and cope with them.

What are night terrors? A night terror is a sleep disorder that occurs during the first half of the night, in the initial slow-wave phase of sleep, when your child is sleeping the deepest. “With a classic case, a child will scream out or cry,” says Judith Owens, M.D., associate professor of pediatrics at the Warren Alpert Medical School of Brown University and a member of the National Sleep Foundation’s Pediatric Sleep Task Force. A night terror can be scarier for you than your child because she won’t even know she’s having one. During a night terror, a child doesn’t wake up, won’t respond to soothing or comforting, or remember the episode the next day. Although screaming is a classic sign, a night terror can also take subtler forms. A child may just mumble or appear slightly agitated. Her eyes might even be open. An episode can last as long as five minutes before a child returns to normal sleep.