Serotonin is probably the neurotransmitter that most of us are most familiar with.  Serotonin affects our mood, sleep cycles and anxiety levels.  The most familiar medications for depression (Prozac, Wellbutrin, etc.) are designed to increase serotonin levels in the system.  According to the book "5-HTP" by Michael Murray, N.D., if serotonin levels are low, the following symptoms may be apparent:  Depressed, anxious, irritable, impatient, impulsive, abusive, short attention span, scattered, flying off the handle, reactive, craves sweets and high carb foods, insomnia and poor dream recall.  Along with the above symptoms, according to the author, the following conditions are also associated with low serotonin levels:  Aggression alcoholism, attention deficit disorder, bulimia, chronic pain disorders, epilepsy, headaches, hyperactivity, muscle twitching, obesity obsessive-compulsive disorder, panic disorders, premenstrual syndrome, schizophrenia, seasonal affective disorder and suicidal thoughts and behavior.  This long list makes it apparent as to why so many people are turning to medication to feel better.  When the above issues become chronic, they affect daily life and the quality of that life.  Many times, low serotonin levels can be hard to determine, because each person displays different symptoms and concerns.  Fortunately, we don't have to suffer with the above issues.  I would recommend seeing a natural health practitioner or your regular doctor to determine what the best solution is for you.  Have a great day - Shanna