Sleep Deprivation: What Happens When You Do Not Get Enough Sleep?
Everyone has felt it: the foggy morning after a bad night. When short sleep becomes routine, the effects pile up in ways that are easy to miss, especially because tired people are poor judges of how impaired they are.
Key takeaways
- Short sleep harms attention, mood, memory and reaction time.
- Long-term sleep loss is linked with higher risks of several health conditions.
- Drowsy driving is dangerous; do not drive when you are struggling to stay awake.
What you notice first
After a short night or two, most people feel slower and less focused, with a shorter fuse and a craving for sugary food. Microsleeps, lapses of a few seconds when your brain briefly switches off, can happen even when your eyes are open, which is why drowsy driving is so risky. Studies have found that being awake for 17 to 19 hours can impair performance about as much as a blood alcohol level of 0.05 percent.
Effects on mind and body
- Thinking: poorer attention, working memory and decision-making.
- Mood: more irritability, anxiety and low mood.
- Appetite: stronger hunger and cravings. See sleep and weight loss.
- Immunity: poor sleep is linked with catching more colds.
Over months and years
Long-term short sleep is associated with higher risks of high blood pressure, heart disease, type 2 diabetes and depression. These are associations from large studies, and many things contribute, but the pattern is consistent enough that major health organisations recommend at least seven hours for adults.
Are you sleep deprived?
If you need an alarm and several snoozes, fall asleep within minutes of lying down, nod off in meetings or rely on caffeine to function, you may be. Check your sleep gap with the sleep debt calculator.
What to do
Start by protecting more time in bed, then work on quality. Gradual recovery is covered in our guide to fixing sleep debt. If you cannot sleep even with enough time in bed, or you snore heavily, speak to a doctor.
Frequently asked questions
How many hours without sleep is dangerous?
Impairment builds from the first sleepless night. Very long periods without sleep can cause hallucinations and serious mental effects, and a person who has been awake all night should not drive.
Can you function on 5 hours of sleep?
Some people feel okay for a while, but studies show that people underestimate their impairment when sleep restricted. Most adults need seven or more hours.
References and further reading: Williamson and Feyer, 2000, Occupational and Environmental Medicine (prolonged wakefulness and performance); Watson et al., 2015, Sleep (AASM and SRS consensus statement).