Hypersomnia, along with many other sleep disorders, is diagnosed using polysomnography. Polysomnography (PSG) is a comprehensive recording of the biophysiological changes that occur during sleep. The PSG monitors many body functions including brain (EEG), eye movements (EOG), muscle activity or skeletal muscle activation (EMG) and heart rhythm (ECG) during sleep.
So basically, I was wired up like a cyborg and had my vitals measured over an evening and then the next day in a hospital laboratory. Hypersomnia is very similar to narcolepsy; the only difference is that hypersomnia sufferers don’t have cataplexy (sudden loss of muscle tone).