Nightmares. We've all had them, and safe to say, we all probably found them to be quite an unpleasant experience.
But it's a whole different kettle of fish when it comes to kids. Surely every parent in the nation with at least a toddler-aged child is familiar with the sound of a panicked scream in the night, or has fielded a request to check for a monster under the bed. Nightmares for adults are scary. Nightmares for kids can be downright terrifying.
But is your child having a nightmare or a night terror? Is there a difference? And how should you, as a parent, react?
First of all -- nightmares and night terrors are very different things, and occur in totally separate cycles of sleep.
"Sleep is divided in basically two aspects -- dream sleep or REM sleep, and non-dream sleep or non-REM sleep," Dr Dev Banerjee, sleep specialist at St Vincent's Hospital, told The Huffington Post Australia.
"Interestingly, the reason it's called Rapid Eye Movement (REM) sleep is because if you put sensors above and below your eye during this stage of sleep, your eyes move left to right, left to right like windscreen wipers.
"In non-dream sleep or non-REM sleep, your eyes don’t move, they are nice and still. Instead, what you see during this phase is the brainwaves are quite slow. They are up and down like waves of water, and that's why the other term we use for non-REM sleep is slow wave sleep.
"Night terrors occur specifically in slow wave sleep. They do not occur in REM sleep.
"Nightmares, on the other hand, occur in REM sleep and not in slow wave sleep."
Okay... but why does it matter in which stage of sleep they happen? A bad dream is a bad dream, right?
Kind of -- but not really.
"If you are in REM sleep or a dream sleep and you suddenly wake up from a bad dream, you have complete recall," Banerjee said.
"It's the situation where you say, 'Oh my god there was someone at the end of the bed who had shining teeth and then he turned into a rabbit' -- you basically remember everything about the dream.
"Nightmares are basically bad dreams that cause a response of fright, flight, and adrenaline rush. But you do have complete recall. You think it’s so real that someone was at the end of the bed with a knife and so on, and it's in this instance you may have a child running down the hall and wanting to climb into bed with you because they have just had a nightmare.
"Night terrors, from a parent's point of view, look to be just as similar in presentation. Your child might look like they've woken up and started screaming, looking like they are completely inconsolable, but in actual fact they haven’t woken out from the dream. They will have no recall of why they have suddenly woken up.
"Essentially, the next morning, if you ask a child who has had a nightmare why he woke up suddenly the night before, he will say, 'oh I had a terrible dream and there was the bogeyman at the end of my bed' and so on.
"If you ask a child who has had a night terror the same question, he or she will say 'Did I? I don't remember that'."
Child & Educational Psychologist Andrew Greenfield says, as tough as it might be for a parent to witness their child having a night terror, it's best if you refrain from waking them up.
"Night terrors are generally harmless and most of the time will end up in deep sleep," Greenfield told HuffPost Australia.
"Generally, children are quite scared if you wake them up. Of course, you'd want to try and protect them from any potential injury if they are thrashing around, but the best thing to do is to not try to wake them.
"Night terrors don't hurt them, they are completely harmless, and are actually more associated with a very deep sleep than a nightmare."
So while night terrors are essentially associated with very deep sleep (in fact, Banerjee puts it in the same category as sleepwalking), nightmares occur in a lighter level of sleep, meaning the child will most likely wake up frightened.
"Nightmares are basically a scary dream that wakes the child, and they will be very awake and very scared," Greenfield said.
"As a parent, you want to comfort them and reassure them -- though don't go into it too much at the time, or they will just get more and more awake -- but you'll want to provide them with any security blanket that might help, such as leaving the lights on or the door open.
"It's important to set good bedtime routines. Try not to let kids associate with too many scary stories or movies or watching the news right before bed. Or if they do happen to catch something unsettling, make sure you watch something more soothing afterward, so the nicer images are in their mind as they go to sleep."
Interestingly, because they occur at different stages in the sleep cycle, nightmares and night terrors tend to take place at different times of night.
"Deep, slow wave sleep tends to happen in the early part of the night," Banerjee said. "Whereas dream sleep occurs in the later or middle part.
"As such, night terrors will usually occur in the first hour and a half after the child has fallen asleep. So if they go to bed at nine, the night terror will happen before midnight.
"Conversely, nightmares are more likely to occur in the middle of the night."