During sleep we experience two patterns of sleep namely non- REM sleep (randomised eye movement) and REM sleep, which follow one another in episodes. The first sleep is non-REM sleep, which is characterised by slow EEG (electroencephalogram) wave pattern, and it makes about 80% of the total sleep. This sleep improves the performance.
Disturbances in non-REM (NREM) sleep results in insomnia and narcolepsy. Insomnia is, difficulty in falling sleep, and the narcolepsy refers to falling in sleep during the day time.
Thus, the blanks can be filled with insomnia; narcolepsy.