Sleepiness can be described as an increased urge to sleep and growing inability to stay awake without feeling a decrease in one's physical energy levels. Unlike sedation, this effect does not necessarily decrease physical energy levels but instead decreases wakefulness, resulting in a propensity for tired, clouded, and sleep-prone behavior. This can lead into a decreased motivation to perform tasks, as the increase in one's desire to sleep begins to outweigh other considerations. Prolonged exposure without appropriate rest can lead to cognitive fatigue and a range of other cognitive suppressions.
Compounds within our psychoactive substance index which may cause this effect include: