'Poor sleepers' are taking roughly two weeks off work every year due to sleep-related ill health, new research suggests.
Yet almost two thirds (60%) don't actually seek help for their sleep problem.
The 'World Sleep Survey' from Big Health found that poor sleep can impact heavily on concentration levels, a person's ability to finish work and their ability to stay awake during the day.
It can also affect energy levels and relationships with other people.
The research was published to coincide with World Sleep Day on 18 March.
It is estimated that one in three people in the UK currently suffer from sleep problems.
A survey of 2,500 people in the UK looked at the impact lack of sleep could be having on the UK's 5.4 million businesses.
It found that the three top issues affecting a person's work due to poor sleep were: concentration (46%), ability to complete work (38%) and staying awake during the day (27%).
Meanwhile the top three personal areas most impacted by poor sleep were energy levels (60%), mood (48%) and relationships with other people (35%).
Peter Hames, CEO and co-founder of Big Health, the creators of sleep improvement app Sleepio, said: "Poor sleep is the unspoken productivity killer in the workplace and it has been ignored for too long.
"Now is the time for employers to wake up to the problem of sleep - improving employee’s sleep positively impacts workplace effectiveness and general wellbeing."
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The average UK employee loses 8.5 days of work a year due to poor sleep.
However 'poor sleepers' - those who rated their sleep quality as below average - miss a staggering 14.6 days of work per year.
It is estimated that absence due to sickness and working-age ill-health, including poor sleep, costs the UK economy £100 billion a year.
Poor sleep has also been linked with mental health conditions such as anxiety and depression.
Colin Espie, co-founder of Big Health and professor of sleep medicine at the University of Oxford, added: "World Sleep Day is the perfect time to acknowledge the widespread effect poor sleep has on our lives.
"Sleep is not an optional extra in life; it is a fundamental requirement.
"The consequences of a bad night’s rest affect us not only physically but also mentally and emotionally, seriously impacting our performance at work.
"Physically we will feel lethargic, mentally we become slowed down with poorer concentration and memory, and emotionally we may become irritable and rather down, with bursts of hyperactivity."
He added: "In terms of daily life, no aspect of daily functioning is unaffected by sleep - least of all our jobs."