People suffering from nightmares wake up in cold sweat and with their hearts pumped up… all symptoms of fear. But a new study suggests that nightmares come in different intensity and are rooted in other emotions.

In the study published in the journal Sleep, researchers wanted to know the differences between bad dreams and nightmares. They asked 572 volunteers to record their dreams for 2–5 weeks. Of the 9,796 dreams recorded, 431 instances were bad dreams while 253 were nightmares.

After analysis, the researchers found out that those who categorised their dreams as ‘bad dreams’ did not feel fear. One-third of those who categorised their dreams as ‘nightmares’ also said they did not feel fear. The prevailing feelings related to both types of dreams were found to be: guilt, sadness, confusion and disgust.

In addition, those who said they had bad dreams generally dreamt about interpersonal conflicts. On the other hand, physical aggression was a big theme among those who said they had nightmares. Intense nightmares also force people to wake up.

Other themes and characteristics of nightmares include death, health concerns, threatening and menacing atmospheres.

The researchers concluded that although bad dreams and nightmares have the same mechanism, nightmares are rarer and more severe.