Drowsiness negatively affects driving, as it causes an **increase in reaction time**. This means that when a person is sleepy, it takes longer to respond to situations on the road, which can be dangerous.

- Drowsiness can be caused by several factors, such as sleeping fewer hours than usual, changing sleep schedules, or driving after eating. It can also be triggered by alcohol or medication consumption, or by sleep-related illnesses.

- The effects of drowsiness include not only increased reaction time but also difficulties in making decisions and performing movements, which can lead to falling asleep for a few seconds without realizing it.

- It is important to note that it is not necessary to fall completely asleep for drowsiness to affect driving. Symptoms such as tiredness and heaviness in the body can appear before falling completely asleep and are already enough to increase the risk of accidents.

Therefore, it is crucial to be alert and well-rested when driving to avoid these risks.