Lack of sleep is a common complaint but for many, falling asleep involuntarily during the day poses a very real and dangerous problem. A new study from the Montreal Neurological Institute (MNI) at McGill University demonstrates interestingly, that sleep-wake states are regulated by two different types of nerve cells (neurons), melanin-concentrating hormone (MCH) neurons and orexin (Orx) neurons, which occupy the same region of the brain but perform opposite functions.