Hypersomnia is a condition characterized by excessive daytime sleepiness where a person may fall asleep during work, eating, or conversations. It can be caused by drug or alcohol abuse, head trauma, certain medications, depression, obesity, or neurological conditions like multiple sclerosis or epilepsy. Parasomnias refer to abnormal behaviors that occur during sleep and don't cause insomnia or sleepiness. They involve partial arousals or abnormalities in sleep-wake transitions. Examples include sleep terrors in children characterized by screaming and intense fear, and restless leg syndrome in the elderly causing urges to walk to relieve feelings in the calves and thighs every 15 to 40 seconds during sleep.