Sleeping on the job is a necessary reality for many nightshift workers, but a new study suggests that instead of providing an energy boost, a night-time nap might put workers at risk.

Research on sleep inertia (the state you are in when you first wake up) by the University of South Australia’s Centre for Sleep Research PhD candidate Cassie Hilditch has particular relevance for nightshift workers in safety-critical industries such as health care or transport, who have to return from breaks and operate at full capacity.

“Sleep inertia is the groggy feeling most people experience when waking up, and is characterised by slow reaction times, poor decision-making and reduced information processing,” Hilditch said.

“This doesn’t matter for people getting dressed in the morning, but for workers in industries such as aviation, petrochemicals, transport and health, post-nap alertness is critical for workplace safety.”

Hilditch’s study found a 30-minute nap during a nightshift produced long-lasting sleep inertia, with recovery times of up to 45 minutes.

A 10-minute nap during a nightshift, however, helped stabilise performance during the hour after waking, with little-to-no sleep inertia.

Hilditch said her research shows the importance of workers allowing time between a nap and the recommencement of work.

“Our research suggests that if you have a 30-minute break in a shift at night, it’s better to take a 10-minute nap at the start of your break. Don’t take a 30-minute nap if you need to return to work straight away,” Hilditch said.

“Our participants were well-rested before the study, so these are likely to be best-case figures, as shift workers may already have cumulative fatigue which could prolong recovery from sleep inertia. In the real world, people are carrying a lot of sleep debt.”

Cognitive tests also revealed participants tended to overestimate their abilities after a nap, with the gap between perception and reality producing further risk.

“If sleep inertia persists beyond your break, and you think you’re more alert than you actually are while, say, operating heavy machinery, then there is a clear safety risk,” Hilditch said.

“One of the challenges is getting people to recognise their limitations. Shift workers might think that since they’ve been doing shift work for six years they are fine, but they might not be – many studies support this.”

Hilditch’s findings may also have an implication for desk-based jobs.

“Lawyers or people in finance might work super-long hours, and their decision-making is just as impaired as the next person’s; it’s just that the risk is financial,” she said.

Prior to her PhD, Hilditch spent five years working for a research consultancy in London, undertaking fatigue-related research in safety-critical industries. In this role she developed fatigue risk management systems in settings ranging from the Libyan desert to the Swiss Alps.

“Trying to give people advice on how to schedule shifts made me realise we don’t know enough to provide all the details,” Hilditch said.