Most of us have pulled an all-nighter at least once. It feels like nothing more than a heavy head the next day. But inside, your brain and body change faster than you might think. Here is what science says happens, step by step.
After 17 to 24 hours: like having a drink
Research summarized by the U.S. National Institute for Occupational Safety and Health (NIOSH, part of the CDC) compares tiredness to alcohol. Being awake for 17 hours affects you about as much as a blood alcohol level of 0.05%. After 24 hours awake, the effect is similar to 0.10%, which is above the legal driving limit in the United States.
At this point it gets harder to focus, remember new things and react quickly. Many people also feel more anxious, irritable or “off”. Mistakes and near misses become more likely, especially behind the wheel.
After about 36 hours: microsleeps
The urge to sleep becomes very strong. Your brain may start taking microsleeps: tiny moments of sleep that last only a few seconds, often without you noticing. Mood can swing more easily, and stress becomes harder to handle.
After about 48 hours: the senses start to play tricks
According to the Sleep Foundation, hallucinations become likely after around two days without sleep. Vision can blur or double, and people may see, hear or feel things that are not there. The world can start to feel strange or unreal.
After 72 hours: the body can barely keep going
Only a small number of studies have followed people who stayed awake this long. In them, people began to slur their words and walk unsteadily, and their sense of reality became badly distorted. At this stage most people simply cannot stay awake on their own.
The most famous case is Randy Gardner, a 17-year-old student who stayed awake for about 11 days in 1964 for a school science project. Experiments like his are no longer encouraged, because staying awake that long is risky.
The good news: sleep repairs most of it
For healthy people, the effects of one short stretch without sleep usually fade after a proper night of rest. The bigger concern is losing sleep night after night. The CDC recommends that adults get at least 7 hours of sleep, yet about one in three U.S. adults regularly gets less than that.
In short
- 24 hours awake affects you about like a 0.10% blood alcohol level.
- Around 36 hours, microsleeps can appear without you noticing.
- Around 48 hours, hallucinations become likely.
- Adults need at least 7 hours of sleep a night.
Sources
- CDC / NIOSH: Work hour training, sleep and impairment
- Sleep Foundation: How long can you go without sleep?
- CDC: Sleep and sleep disorders
This article is for curiosity and learning only and is not medical advice. If you have trouble sleeping, talk to a doctor.