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It was originally thought that the nap on E1 should primarily contain [https://en.wikipedia.org/wiki/Rapid_eye_movement_sleep REM] to ensure a successful adaptation. However, according to the Polyphasic Survey 2018<ref name="polysurvey" />, only 50% of adapted E1 sleepers managed to get REM in their nap. This shows that the afternoon nap is not guaranteed to deliver REM sleep. Based on the data above, it still seems possible to complete the adaptation to E1 with no REM in the nap. This is likely a result of those adaptees covering their REM need by their core, leaving their nap as just wakefulness sustainment.

It was originally thought that the nap on E1 should primarily contain [[wikipedia:Rapid_eye_movement_sleep|REM]] to ensure a successful adaptation. However, according to the Polyphasic Survey 2018<ref name="polysurvey" />, only 50% of adapted E1 sleepers managed to get REM in their nap. This shows that the afternoon nap is not guaranteed to deliver REM sleep. Based on the data above, it still seems possible to complete the adaptation to E1 with no REM in the nap. This is likely a result of those adaptees covering their REM need by their core, leaving their nap as just wakefulness sustainment.

==Adaptation== <!--T:7-->

==Adaptation== <!--T:7-->

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Another common issue is the rather common [[Special:MyLanguage/stage 3/4 loop|stage 3/4 loop]] for beginners. This typically happens when a sleeper cannot complete the adaptation and get stuck in [[Special:MyLanguage/4-Stages Adaptation Model#Stage 4|Stage 4]] where, near the end of adaptation, the sleeper feels inconsistently adapted, excessively tired at certain times of the day, or [[Special:MyLanguage/sleep inertia|sleep inertia]] upon wakes. Because E1 likely has sufficient total sleep to gain all the needed [https://en.wikipedia.org/wiki/Slow-wave_sleep SWS], being trapped in Stage 4 may be due to a slight REM deficit. A potential method to address this issue has been proposed, covered in [[Special:MyLanguage/#slightly-modified core length|6.5h core variant]] section.

Another common issue is the rather common [[Special:MyLanguage/stage 3/4 loop|stage 3/4 loop]] for beginners. This typically happens when a sleeper cannot complete the adaptation and get stuck in [[Special:MyLanguage/4-Stages Adaptation Model#Stage 4|Stage 4]] where, near the end of adaptation, the sleeper feels inconsistently adapted, excessively tired at certain times of the day, or [[Special:MyLanguage/sleep inertia|sleep inertia]] upon wakes. Because E1 likely has sufficient total sleep to gain all the needed [[wikipedia:Slow-wave_sleep|SWS]], being trapped in Stage 4 may be due to a slight REM deficit. A potential method to address this issue has been proposed, covered in [[Special:MyLanguage/#slightly-modified core length|6.5h core variant]] section.

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