Speaking at the British Science Festival, Professor Mark Blagrove explains that these findings support other research he's been working on that has found "you tend to dream of emotional things that have happened to you."

Blagrove's other research has looked at recurring dreams and suggests that these help us process and commit information to our long-term memory.

He explains that a one-off dream is just a way of processing recent experiences.

“If you dream of important things that happen in the day, it maybe just a residual consequence of things that happened to be in your mind and nothing of any consequence at all."

Whereas if you have another dream on the same events, it usually becomes more abstract when it recurs five to seven days later. So much so that independent judges given transcripts of the dreams and diaries from the participants of their waking lives were unable to match them to the real event.

This dream lag effect is "very difficult to explain" he states, but is evidence that the brain is doing something to process memories.

Blagrove also supports the idea that nightmares are what happens when your brain fails to make sense of information, and "just cannot do the linking and interconnecting."

This he says is why "a trauma will recur in dreams and it’s not made into a kind of metaphor in which you start to make sense of things.”

As for why we often can't remember dreams, he says it's not worth worrying about.

“It could be we have evolved to forget them very quickly. It could be it’s best not to know.”

Study shows dreams help us to remember what's most important to us