For so long we've been told that a solid, relaxing, refreshing block of seven-to-nine hours sleep is the optimal amount required every day for a top functioning body and mind. But often that seven-to-nine hour evening stretch is far from relaxing or refreshing but instead filled with sweat-inducing nightmares ranging from having to redo your high school certificate because you didn't graduate after all or having to immediately present a huge work assignment you can't remember getting or trying to save someone just a few feet away but the dreamscape air is so heavy you can't seem to move. Nightmare-filled sleep leaves us feeling exhausted and demented which is why science has been trying to find a cause (and cure) for so long.

According to New Scientist most nightmares occur after upsetting events so most of the research so far focused on studying people suffering from things like post-traumatic stress disorder (PTSD), but not everyone suffers from PTSD, so how to explain that pretty much everyone has a nightmare or three at some point in their life?

A team of researchers from the University of Oxford's Psychiatry department led by Stephanie Rek set out to answer this question with a study of nightmares in the general UK population. Their research found that while stress is a major cause of nightmares, the duration of sleep is also a surprising contributor to those scary shut-eye montages. Specifically, sleeping more than nine hours each night, according to the New Scientist article, "might increase the amount of late-night rapid eye movement (REM) sleep - the time when nightmares most commonly occur."

In an interesting twist for the wine-lover and exercise fiend the study also found, "...alcohol use and physical activity levels were not associated with nightmares."  

Doing the maths it sounds like that seven-to-nine hours sleep rule might need to be updated to seven-to-eight if we're looking for a proper refreshing kip.

Scared to sleep? Science says this is what causes nightmares