This Just In from: pointofreturn.com

But elevated serotonin triggers the production of Cortisol and Adrenaline (Epinephrine), which is the body's natural reaction from the body to combat the excess Serotonin levels. This is what gives the boost or euphoric state that can last for a period of time. However, as Serotonin remains unnaturally high, the adrenals become fatigued and cause levels of Adrenaline to decline while the Cortisol increases. The adrenals become exhausted, which helps to explain the fatigue and other symptoms that many SSRI-Antidepressant users report.