Among sleep-related concepts with high closeness ratings, insomnia, sleep apnea, narcolepsy, and restless legs syndrome stand out. Hormones like melatonin and cortisol regulate sleep, while neuropeptides such as orexin and hypocretin promote wakefulness. External factors, including genetics, medications, and lifestyle choices, can impact sleep quality. Treatment options range from CPAP therapy and oral appliances to surgery, and their effectiveness varies based on the underlying cause of the sleep disorder. Resources like the American Academy of Sleep Medicine and National Sleep Research Project provide support and information for individuals seeking to improve their sleep health.