During which part of the night do nightmares typically occur?

Nightmares typically occur during the last third of the night, particularly during the REM (rapid eye movement) sleep phase, which becomes more prominent in the later part of the sleep cycle. As a person progresses through the night, REM sleep—when most dreaming occurs—becomes longer and more frequent, increasing the likelihood of experiencing vivid dreams or nightmares. This is why the last third of the night is crucial for recognizing when nightmares are most likely to happen.

The other options are contextually less accurate since nightmares are not commonly reported or associated with sleep phases occurring in the first hour, middle of the night, or throughout the entire night. During the initial part of the night, sleep is primarily comprised of non-REM stages, where the chances of having nightmares are significantly lower. Therefore, recognizing the timing of REM sleep helps understand why the last third of the night is the most critical for nightmares.