A sleep lab study is a type of research that focuses on the study of sleep. It typically involves monitoring and recording the physiological processes that occur during sleep, such as respiration, heart rate, and brain activity. Apnea, which is a five-letter term, is a condition in which a person stops breathing for short periods of time during sleep. REM, which is a three-letter term, stands for Rapid Eye Movement and is a stage of sleep characterized by increased brain activity and eye movement.