An estimated one in seven (12 per cent) UK drivers suffer from health or sleep disorders, it has been found.
According to a survey by road safety charity Brake, 12 per cent of motorists have "head-nodded" - or fallen asleep for up to 30 seconds - behind the wheel during the past 12 months.
The organisation and Cambridge Weight Plan have warned in a new report that many people could be doing so because they are suffering from underlying health complaints such as sleep apnoea, which can interrupt their nightly rest.
Treatment for sleep disorders could help such individuals as the condition can cause daytime tiredness and in severe cases can lead to sufferers nodding off without warning.
"We still have widespread misunderstanding of how to prevent driver tiredness and ignorance about factors like sleep apnoea, a condition that can be treated," the organisation's campaigns director Julie Townsend stated.
Driving Standards Agency deputy chief driving examiner Sandra Dodson responded to the report by urging commercial drivers to take regular breaks and walk around to reduce sleepiness.