I believe the lay person has a different concept of the role of serotonin. Yes it is the happy hormone, but it is much more than that.
Serotonin is the neurotransmitter brain chemical that is actually mostly produced in the GI tract. The neurotransmitter is taken up by the brain through the brain gut neuropathways which can affect other neurotransmitter levels as epinephrine, GABA and dopamine.
Recently a paper was published about serotonin levels in post-epileptic patients. Significant changes were noted in serotonin following generalized seizures. There was a correlation between serotonin levels and seizure duration. It was a multicentered trial published in the journal Epilepsia.