It can hit as you are driving home from work, on a long trip or in a traffic jam – the feeling that you cannot resist falling asleep.
But closing your eyes even for a second while driving can be dangerous for yourself and others, says German testing organisation Dekra.
If you are driving at 120 kilometres (75 miles) per hour, you are covering more than 33 metres (36 yards) in a second. That adds up to more than 100 metres in three seconds.
If your eyes close while you cover that distance, you avoid an accident only if you are lucky, says Dekra accident researcher Markus Egelhaaf.
For Germany, the official 2023 crash statistics state fatigue as the cause of 1,902 traffic accidents resulting in personal injury, in which 3,010 people were injured – 42 of them fatally.
The number of crashes caused by driver fatigue could be much higher, experts say, since drivers often do not admit to being overtired or it cannot be proved.