Waking up is the process of transitioning from sleep to wakefulness. This occurs when the body’s internal clock, or circadian rhythm, signals that it is time to become alert. During this time, the brain becomes more active, and the body starts to function, including increased heart rate and blood flow. The act of waking up can be influenced by various factors, such as light exposure, alarm clocks, and sleep cycles. People often experience different levels of alertness upon waking, which can be affected by the quality of their sleep and the duration of their rest.