“The reason is the way your circadian rhythms work – melatonin makes you go to sleep and stress hormones wake you up. So if you already have higher stress hormones from confinement stress or other factors, a high waking heart rate represents your overall chronic stress level,” she says. If your waking heart rate increases over time, your coping strategies might need to be improved.

Expect conflict to happen

It was also around the six-month mark on Dunn’s mission that people started getting more confrontational and more likely to air their frustrations. Researchers call this the “third quarter phenomenon”, when people completing missions in challenging conditions, like astronauts, report a drop in morale.

“The third quarter phenomenon can start around the halfway point,” says Dunn, “People begin to feel there isn’t really an end in sight and the novelty of everything is gone. You might need to find some intrinsic or extrinsic motivation to keep you on good behavior and on better terms with the people you live with.”