During which sleep disorder do sufferers may lapse directly into REM sleep?

The correct answer is narcolepsy, as this sleep disorder is characterized by sudden and uncontrollable episodes of deep sleep during the day. Individuals with narcolepsy may fall directly into the REM stage of sleep, bypassing the typical progression through the different sleep stages that most people experience. This can lead to situations where the person might suddenly doze off during activities, and these abrupt transitions into REM sleep can also result in vivid dreams and disrupt normal alertness levels.

This is in contrast to sleep apnea, which involves interruptions in breathing during sleep; night terrors, which are episodes of extreme fear or panic during non-REM sleep that typically occur in children; and insomnia, which is characterized by difficulty falling or staying asleep. All these disorders involve different mechanisms and stages of sleep disruptions that do not include the direct transition into REM sleep that is seen in narcolepsy.