1. consciousness: a state of awareness, including a person’s feelings, sensations, ideas, and perceptions

2. REM sleep: a stage if sleep characterized by rapid eye movements, a high level of brain activity, a deep relaxation of the muscles, and dreaming

3. circadian rhythm: the rhythm of activity and inactivity lasting approximately one day

4. insomnia: the failure to get enough sleep at night in order to fell rested the next day

5. sleep apnea: a sleep disorder in which a person has trouble breathing while asleep

6. narcolepsy: a condition characterized by suddenly falling asleep or feeling very sleepy during the day

7. nightmares: unpleasant dreams

8. night terrors: sleep disruptions that occur during Stage IV of sleep, involving screaming, panic or confusion

9. sleepwalking: walking or carrying out behavior while asleep