Are sleep cycles always 90 minutes?
Average 85-120 minutes. Duration varies by individual, age, sleep debt. 90 is serviceable estimate; consistency matters more than precision.
Why do I feel groggy waking mid-cycle?
Deep sleep stages have reduced arousal. Waking during disrupts neural consolidation; takes 20+ minutes to feel alert. Between-cycle waking (light stage) allows rapid arousal.
Is this calculator scientifically proven?
Sleep architecture research confirms cycle concept. Real-world effectiveness varies; environment, caffeine, stress influence actual grogginess despite aligned timing.
How much time until sleep starts after bed?
Sleep onset latency averages 10-20 minutes. Calculator assumes middle of range. Track your typical lag and adjust bedtime if needed.
What about naps and sleep cycles?
Short naps (20-30 min) avoid deep sleep grogginess. 90-min naps hit full cycle. Longer afternoon naps impair nighttime sleep.
Does caffeine affect cycle timing?
Caffeine doesn't change cycles but fragments sleep, shortening total duration and deep-stage time. Avoid after 2 PM.
Is 5-6 hours ever optimal by cycles?
5-6 hours skips some deep/REM sleep despite cycle alignment. Aim 6-9 hours for adequate restorative stages.
Why wake groggy despite ideal timing?
Sleep debt, poor sleep quality, stress, light exposure, caffeine late-day override optimal timing. Holistic sleep hygiene essential.
Do cycles shift with age?
Yes. Older adults have shorter, lighter cycles and less deep sleep. Adjust expectations and bedtimes accordingly.
Should I prioritize cycle alignment or total sleep?
Total duration matters most. 8 hours mid-cycle beats 5 hours well-timed. Optimize both when possible.