**Drowsiness** in a driver can be caused by several factors, and one of them is **changing usual sleep hours**. This means that if you alter your sleep routine, for example, by sleeping at different times than usual, you may experience drowsiness while driving.

- **Changing sleep hours** affects the circadian rhythm, which is the body's internal clock. This change can cause a feeling of **tiredness** and **heaviness in the body**, even if you have slept enough hours.

- Drowsiness is not only caused by sleeping few hours, but also by **sleeping at unusual times**. This can make you feel less alert and more prone to making mistakes at the wheel.

- It is important to recognize the **symptoms of drowsiness**, such as difficulty keeping your eyes open, blurred vision, or losing concentration. These symptoms can appear before you fall completely asleep, increasing the risk of accidents.

Therefore, to avoid drowsiness while driving, it is crucial to maintain a regular sleep schedule and not alter the times you usually sleep.