Three neurotransmitters (dopamine, serotonin and norepinephrine) appear to work together for individual well-being. Serotonin is an inhibitory neurotransmitter. It balances any excessive stimulating. neurotransmitter firing. Serotonin is important for managing mood, appetite, sleep, and dreaming. If your serotonin levels become low, one may become irritable, anxious, depressed, and have trouble sleeping. Dopamine is most famous for its stimulant and pleasurable effects. Dopamine is considered to be both excitatory and inhibitory. Norepinephrine is similar to dopamine in that it also produces alertness, focus and motivation. Low levels of norepinephrine are associated with low energy, decreased focus ability and sleep cycle problems.