Drowsiness, also referred to as hypersomnia, is excessive daytime sleepiness. Anything that affects nighttime sleep duration or interrupts it may lead to drowsiness the following day. One may experience it as a side effect of many drugs, such as allergy medication, sleeping pills, and sedatives. During the state of drowsiness, an electroencephalograph would detect alpha waves. Although it is normal to experience drowsiness every once in a while, medical help is necessary when it is chronic.