Scientists have found that our sense of how fast time passes is partly caused by changes in our bodies.
They found that greater activity of the sympathetic nervous system (SNS) - that is, an increased heart rate and an increase in electrical conduction - had a "minor but significant" effect on feeling time pass more quickly.
It is believed to be the first time that such objective measures of physiological arousal have been studied in relation to time perception.
The researchers asked 67 people to complete normal daily activities while wearing sensors that measured how the sympathetic nervous system behaves.
They wore a heart rate monitor as well as a skin sensor that measured subtle changes in skin electrical conduction caused by activity of the sweat glands.
The participants were asked to report, hourly, how fast or slow they had felt in the last 60 minutes compared to normal.
The researchers then analyzed the participants' biological data along with their personal reports.
"Overall, studies have shown that boredom, social isolation, and stress are associated with slower passage of time, while greater social satisfaction and decreased stress are associated with more rapid passage of time," they wrote in their paper.
On the basis of these findings, it is often assumed that changes in physiological arousal, which often accompany self-reported fluctuations in emotion, play an important role in time distortion, but so far this conclusion has not been tested during real-world activity, using objective measures of physiological arousal.
The study's lead author, Dr Ruth Ogden, from Liverpool John Moores University, said: 'The results show, for the first time that an increase in SNS activity can significantly speed up our subjective experience of time - arousal makes time pass more quickly. Heart rate, it can make that time seem to pass by up to 10%.”
She explained that if they had gone through more ups and downs, the effect would likely be greater, and it was believed that there was an evolutionary benefit behind that.
"Work that I did in the lab using electric shocks and other stimuli showed much greater effects of SNS activity on the experience of time," Ogden said, via findings published in Nature: Scientific Reports.
And when we think about why humans are deformed over time, one idea is that there is some kind of evolutionary benefit to having a flexible timing system — think again about being a caveman, it might be having "extra time" provided some survival advantage.
Assuming this evolutionary survival calculation is correct, it wouldn't make sense to have a timing system that dwindles and dwindles with every small change in excitement.
Instead, it must be a system that reacts to big changes - fight or flight.
The researchers said that feeling that time is passing faster or slower than it actually is can have major impacts on people's well-being.
They said the feeling that we don't have enough time was linked to "lower life satisfaction, poor health outcomes, and risky decision making".