Diagnosing Sleep Apnea, ruling out Narcolepsy

According to the Mayo Clinic, nocturnal polysomnography, a test used to diagnose sleep apnea, "... monitors your heart, lung and brain activity, breathing patterns, arm and leg movements, and blood oxygen levels while you sleep."

Oximetry is another test that monitors the oxygen level in your blood while you sleep to find fluctuations caused by sleep apnea.