**Drowsiness** is a state in which the driver feels tired, heavy in the body, and sleepy. This state can affect the ability to drive safely even before the driver falls completely asleep.

- **Symptoms of drowsiness**: These symptoms appear before the driver falls completely asleep. They include slower reactions, difficulty making decisions, and slower body movements. Additionally, the driver may fall asleep for a few seconds without realizing it.

- **Causes of drowsiness**: Sleeping fewer hours than usual, changing sleep hours, poor sleep, driving on roads with little traffic, consuming alcohol or medications, having sleep disorders, and driving at dawn or after eating can cause drowsiness.

Therefore, accidents can occur **even before the driver is completely asleep**, as the effects of drowsiness affect the driver's reaction and decision-making ability.