Waking up with with a jolt, covered in sweat, fear, sadness... you probably had a nightmare! But why do some of our dreams take this dramatic turn? A team of Swedish, English and Finnish scientists looked into the subject.A scientific studyThey observed 17 healthy adults before they fell asleep, and then during their REM sleep (the best time to dream).'We found that people who had greater brain activity in the right frontal cortex than in the left cortex during wakefulness and paradoxical sleep experienced more anger while they were dreaming," said Dr. Pilleriin Sikka, in the study published in the Journal of Neuroscience, as reported by Relaxnews.A first stepThe increased activity in the right hemisphere promotes the feeling of anger during wakefulness, which appears to have a direct impact on sleep, according to this new research. The negative feelings present while the subject is awake, and later in their dreams, therefore give rise to nightmares.This study has only been conducted only on a small group of people so far, but it's a good starting point to understand the emotions we have in nightmares.You can find more details about the origins of nightmares in the video above.