Sleep
Ultradian Nap Window
An ultradian nap window is the natural mid-cycle alertness dip—often early afternoon—when a short nap restores focus without heavy sleep inertia.
An ultradian nap window is the mid-cycle dip roughly ninety to one hundred twenty minutes after waking when brief rest restores alertness without full sleep inertia. These rhythms repeat across the day; early afternoon often feels deepest.
Match nap length to window—twenty minutes for a boost, ninety minutes only if night sleep is protected. Fighting the dip with caffeine alone can delay night sleep.
Common questions
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How is ultradian timing different from the nap wheel?
Ultradian dips repeat every one to two hours across wake time; nap wheels map broader hours-since-waking sweet spots. Both point to early afternoon for many people.
Related terms
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