Excessive sleepiness or hypersomnia refers to a condition characterized by recurrent episodes of excessive sleepiness during the day or prolonged nighttime sleep sessions. While many people experience tiredness during the day, this is not the same as excessive sleepiness. People with excessive sleepiness are prone to repeated napping throughout the day, often at inappropriate times such as during work or in the middle of a conversation, and the naps do little to provide them with relief. People with excessive sleepiness often find it very difficult to awaken from a long sleep and may manifest other symptoms such as irritability, mental confusion, decreased energy, and memory loss. There are several possible causes for excessive sleepiness.