We've all been there, right? Waking up in the middle of the night in a cold sweat, heart racing, mouth dry, thinking 'holy crap that was a scary dream!'? (You might also be thinking 'surely I'm too old for these' but, sorry, folks, nightmares aren't just for kids.)
So what exactly is a nightmare and what on earth do they mean?
"A nightmare is really the same as a dream, and as with any dream, it reflects the last one to two days of both your conscious and unconscious experiences," dream analyst Jane Teresa Anderson BSc Hons told The Huffington Post Australia.
"The whole point of dream is to try and make sense of your world. A dream is basically your brain processing your experiences and trying to update the hard drive.
"Sometimes we are processing the really lovely stuff in life, sometimes we are processing the challenges (literally having slept on it) and sometimes the really tough stuff -- fears and anxieties, anger and pain."
According to Anderson, a key factor in what makes a nightmare a nightmare is the fact whatever we are processing -- whether that be fear, anger, or another negative emotion -- isn't resolved during the course of the dream.
"Those sorts of things are difficult to resolve in the length it takes to dream," Anderson explained. "Sometimes it can take many dreams or many years to process all this stuff.
"If you resolve the issue, it's less of a nightmare and you will sleep on and wake up feeling fantastic. It's not really a nightmare if there's a fire and you put it out, or a monster and you faced it. Chances are you will wake up thinking 'I stood up for myself and I solved the issue and it felt great'.
"With a nightmare, you generally wake up still feeling frightened, because the issue remains an issue and hasn't yet been resolved."
Anyone who has ever had a nightmare will agree one of their defining features (aside from being scary) is that they feel so real.
"This is because the body produces the fear hormones or stress hormones exactly as if you were wide awake during the day," Anderson said.
"In your dream, your physiological body is responding by producing the hormones adrenaline and cortisol exactly as if you were awake. Your heart starts to pound, goosebumps come out, you can get anxious and stressed. In fact, you usually wake up from the dream because of your body's response.
"So when people say 'I know it was a dream, but it felt really real' -- it felt real because your body was actually going through reactions."
In terms of what your nightmare actually means or says about you, Anderson says the best way to start interpreting it is to figure out how it made you feel.
"So, one very common nightmare is when you feel you are being trapped in one sense or another," Anderson said.
"Trapped in a fire, trapped by a tsunami, trapped by a terrorist... whatever the scenario, the general feeling is 'I'm feeling trapped, I can't get out'.
"Because you know a dream is trying to process the last one to two days, the first thing I would do is ask myself 'where in my life was I feeling trapped during that period?'
"It could be trapped in any sense of the word -- trapped by a relationship, trapped in your job, trapped by own negativity. But that is what you'd be looking for.
"On the flip-side, you might be the sort of person who'd say, 'I never feel trapped. I always feel really free. No one can ever corner me, I'm always in control, I can manipulate any situation to suit me.' What's happening here is your nightmare is a reaction to your unconscious fear of entrapment."
Do you find yourself having the same bad dream over and over? Nightmares are often recurring, which Anderson says is once again due to the fact the issue at their core remains unresolved.
"Because you couldn't find a solution -- say the car goes off the edge of the cliff or you can't escape from the fire -- that dream remains unresolved," she said.
"And so the waking life issue also remains, and next time it comes up, your dreaming mind might refer to the same dream again. The fact of the matter is you are stuck in that issue."
In good news, Anderson says there is a technique you can employ to help you banish certain nightmares forever, and all it requires is a little bit of imagination.
"This process is what I call dream alchemy," Anderson told HuffPost Australia. "On a very simple level, it involves you (while you're awake) visualising being back in the dream, only this time you change the dream's ending. So if you are in a speeding car where the brakes don't work, this time, you visualise putting your foot on the brake and bringing the car to a halt. Then perhaps you visualise turning the ignition back on and driving at the speed you want to.
"Have this visualistion of driving the car and imagine feeling inspired and uplifted. Silly though that may seem, you're actually talking to your unconscious mind and reprogramming the way it responds to feeling overworked or being unable to put a stop to something."
While everyone's dreams are undoubtedly unique and reflective of what is going on in their individual lives, there are also some fairly common dreams which Anderson says she hears about again and again.
We had her break down the meaning behind some of these more universal nightmares (we're also betting you've had at least one of these at some point).
No pants at school/work
"Generally, this means you are feeling exposed," Anderson said. "Emotionally exposed or like people can see right through to the 'real me'. You may feel this if you have let your guard down and are not putting on an image, and therefore don't feel as protected.
"If it takes place at school, this can often be your dream brain's way of saying you feel like a child."
Not being prepared
Ever have a dream where you're sitting an exam you haven't studied for?
"This is dealing with beliefs about the errors of coming to something unprepared," Anderson said. "It has to do with your beliefs in success, concerns about failure, concerns about winging it... it's often exploring all of that, even if the person who is having the dream is super prepared in real life.
"So, to use the example of being back at school sitting an exam, my first question would be 'what did you feel?' You may have felt as though you were being tested and didn't know enough. Okay, so when in the past couple of days did you feel like that?
"It could be in your relationship, it doesn't have to be knowledge-based."
"What are you running away from in your life? Usually it comes down to something you don't want to face," Anderson said.
"Interestingly, it's quite common in people who are not looking after themselves from a health point of view. They are running away from taking good care of themselves and that deep knowledge they are not doing their health a big service. 'Maybe I shouldn't be doing drinking as much or taking those drugs' -- that kind of thing.
"It's also common in people who aren't feeling well but who don't want to go to the doctor, or in women who are going through menopause and are trying to ignore the issue."
"Losing teeth is a very common dream scenario," Anderson said. "Particularly when the person is trying to say something and their teeth keep falling out of their mouth and they are finding it increasingly hard to talk... I hear about this all the time.
"Often this symbolises a lack of confidence, that you are losing confidence in something, and for every word you are spitting out you are getting in deeper and deeper."