Is 5 Hours of Sleep Enough? What It Does to You, and How to Get Through the Day

No. Five hours of sleep is not enough for adults, even if you feel OK. Experts recommend at least 7 hours, so 5 hours leaves you about 2 hours short every night. One night won't do lasting harm, but in lab studies, people kept to 5 hours a night got steadily slower and made more mistakes, and a few nights of normal sleep weren't enough to bring them back.

What one 5-hour night does

A single short night mostly shows up as:

• Slower reactions and more lapses, those moments where your attention just drops out.
• Stronger afternoon sleepiness, especially in the early-afternoon dip.
• Shorter temper and flatter mood.
• Less REM sleep. REM is concentrated in the last cycles of the night, so a 5-hour night cuts off much of it.

You'll get through it. The problem is when one night turns into a pattern.

What 5 hours a night does over a week

In a 2003 study at Walter Reed Army Institute of Research, volunteers spent 3, 5, 7 or 9 hours in bed for 7 nights. The 5-hour group's reaction speed dropped over the first few days and then settled at a lower level, and their attention lapses went up.

The part that surprises people: after the week, they got three nights of 8 hours in bed, and their performance still hadn't recovered. The researchers suggested the brain adapts to short sleep in a way that takes more than a few good nights to undo.

A separate study at the University of Pennsylvania found that even 6 hours a night for two weeks left people performing about as badly as someone kept awake for one to two full nights, while they rated themselves only slightly sleepy. Five hours is less than that. For the full picture on the 6-hour version, see is 6 hours of sleep enough.

Why 5 hours can feel fine

• You stop noticing. In the studies above, how sleepy people felt leveled off while their performance kept falling.
• Caffeine hides it, without paying back any sleep.
• You're running on adrenaline. A busy, stressful day can mask sleepiness until you sit still.

A very small number of people genuinely do well on short sleep because of rare genetic traits. If you need an alarm, lean on coffee or sleep in on weekends, you're not one of them.

If you only have about 5 hours: time it to your cycles

Five hours is 3.3 sleep cycles, so your alarm may catch you partway through a cycle. If you're choosing between options on a short night, it can help to round to a full cycle:

• 4.5 hours (3 cycles): less sleep, but you're more likely to wake from lighter sleep.
• 6 hours (4 cycles): better if you can find the time.

Each bedtime below includes 15 minutes to fall asleep.

The sleep calculator does this for any wake-up time. If the choice is between a very short sleep and none at all, see sleep 1 hour or stay up.

How to get through a day on 5 hours

1. Get bright light soon after waking. It helps you feel more alert and keeps your body clock on track.
2. Have caffeine early, not all day. A coffee in the morning is fine. A late one will make tonight worse. Check your cutoff with the caffeine calculator.
3. Take a 10 to 20 minute nap in the early afternoon if you can. The nap calculator sets the alarm.
4. Don't drive drowsy. If you catch yourself yawning, drifting lanes or missing exits, pull over somewhere safe.
5. Go to bed a bit earlier tonight, but not hours earlier. A normal bedtime or up to an hour early usually works best.

How to recover from a run of 5-hour nights

Because recovery is slow, plan for more than one good night. Aim for 7.5 to 9 hours for several nights in a row, keep your wake-up time steady, and avoid huge weekend lie-ins that shift your body clock. The sleep debt calculator shows roughly how much you owe.

If you can't sleep more than 5 hours even when you have the chance, or you're getting 7 or more hours and still exhausted, talk to a doctor. Ongoing insomnia, loud snoring with gasping, or pauses in breathing are all worth checking.