Sleep promotes adequate mental and physical development.
Sleep is connected to numerous elements of physical, emotional, and mental health and provides insights about how people can get better sleep.  
These chemicals include melatonin, serotonin, GABA, orexin, adrenaline, cortisol, and others.
Yes.  A licensed medical professional can review the potential benefits and risks of different types of treatments, including prescription medications and cognitive behavioral therapy.
The basic concept of sleep hygiene may apply to most people but what ideal sleep hygiene looks like can vary based on the person.