Due to our circadian rhythms, we generally experience peak levels of alertness in the morning and early evening. Sleep bank balance. How long you've been awake and how much sleep you've had in recent days affects your alertness level. Ingested nutrients and chemicals. Environmental light .
Bright light tends to increase alertness while dim light leads to drowsiness.
Cool, dry air, especially on your face, helps keep you alert, while heat and humidity make you drowsy. The sound of rolling waves on the beach or the hum of white noise from machines can lull you to sleep. Irregular or variable sounds, such as a radio, conversation or a honking horn, stimulate alertness. Studies have found that some smells like peppermint, make people more alert. Others, like lavender, meanwhile, have a sedative effect.