Our understanding of the cause and treatment of nightmares has totally changed how psychologists treat PTSD.

At the height of the pandemic, a strange phenomenon occurred – people started having weird dreams. The effect seems to have been most pronounced in those particularly affected by the virus and in countries with strict lockdown measures. Concerns about lockdowns, loved ones and personal health were suddenly jumbled up with other mundane thoughts, leaving some waking up in confusion.

For people on the frontline, the dreams became nightmares. Of 114 doctors and 414 nurses working in the Chinese city of Wuhan, who all took part in one study published in January 2021, more than a quarter reported having frequent nightmares.

Reports of nightmares among citizens also rose during national lockdowns, with young people, women and people suffering with anxiety or depression the highest risk. But for people who research trauma, the increase in nightmares was no surprise.

For those on the frontline of Covid-19 responses, like those doctors and nurses in Wuhan, 2020 was a period of “chronic stress”, says Rachelle Ho, a PhD candidate at McMaster University in Canada. Long periods of stress which last months or years and affect whole populations are quite unusual – comparable only to wars in recent history, Ho says – but we know that chronic stress has a significant effect on our cognitive function.

People living under regular duress are more likely to have nightmares. A study looking at schoolchildren aged 10 to 12 in the Gaza strip found that more than half experienced frequent nightmares and on average they occurred on more than four nights per week. Children are particularly susceptible, says Ho, because their brains are still developing.

While nightmares are strongly linked to a host of mental illnesses, some vivid dreams help us to process the emotions of the previous day, says Joanne Davis, a clinical psychologist at the University of Tulsa. Understanding why bad dreams become nightmares is helping to treat people who have experienced trauma.

How bad dreams protect us in waking life

Psychologists like Davis are beginning to unravel the links between our dreams, psychological disorders and their importance in keeping us emotionally stable when in good health.

While we sleep, we organise and file away our memories of the previous day and give our older memories a bit of a dust-off and reshuffle. It is thought that this happens throughout sleep, but it is in the Rapid Eye Movement (REM) stage (just before we awake or as we dip into sleep) that we store our most emotional memories. These emotionally charged memories then become the subject of our dreams.