To be overly simplistic: If dopamine is altered, then one may be out of touch with reality; if GABA is altered, one may be anxious; if Acetylcholine is altered, then one may have memory problems; if norepinephrine is altered, one may be manic high; and if serotonin is altered, one may be depressed, worried, more irritable, and have insomnia.

Serotonin may play a role in depression, anxiety, sleep, sexual issues, eating issues, pain perception, obsessive worry, panic disorders, aggression, and PMS. Norepinephine may play a role in bipolar disorders, depressions, and attention problems. Dopamine may play a role in a loss of touch with reality, attention deficit issues, drug addictions, and in mood, as well. GABA may play a strong role in anxiety and some addiction issues. Acetylcholine plays a role in memory. Histamine may play a role in sleep and weight gain.

http://www.minirthclinic.com/digest-downloadpg1.html