Actor Keerthy Suresh stayed awake for 41 hours. What does that do to you?

“One sleepless night may leave you feeling tired, but staying awake continuously for nearly two days places the brain and body under significant physiological stress,” says Dr Nikhil Modi, Senior Consultant, Respiratory, Critical Care and Sleep Medicine, Indraprastha Apollo Hospital, Delhi. “Sleep is not a luxury. It is a biological necessity that every organ system depends on to function and recover,” he says.

Research has shown that being awake for 17 to 19 hours can impair attention, reaction time and judgement to a degree comparable to having a blood alcohol concentration (BAC) of 0.05%. After about 24 hours without sleep, the impairment may be similar to a BAC of around 0.10% — above the legal driving limit in many countries. As a result, sleep-deprived individuals are more likely to make errors, overlook important details and respond more slowly in situations that require quick thinking.

What happens to your body when you stay awake for too long?

Sleep is often the first thing people compromise when work schedules become demanding. While an occasional late night may not cause lasting harm, prolonged periods of staying awake for extended hours can affect the body’s ability to function normally. The human body follows a natural sleep-wake cycle, and disrupting this rhythm for long durations can have physical as well as mental consequences.

The brain starts slowing down

When a person remains awake for extended periods, the brain’s ability to maintain attention, process information and make decisions begins to decline. Sleep deprivation can affect reaction time, memory and coordination, increasing the risk of mistakes and accidents.

The areas of the brain involved in judgement and emotional control are particularly sensitive to lack of sleep. This can result in mood changes, irritability, reduced concentration and difficulty handling stress.

The danger of microsleep

After 24-36 hours of remaining awake, the brain can briefly “switch off” for a few seconds without the person realising it. One of the biggest dangers of prolonged wakefulness is “microsleep”—brief, involuntary episodes lasting a few seconds during which the brain momentarily falls asleep. A person may appear awake but fail to respond, making activities such as driving, operating machinery or even making important decisions potentially dangerous.

Hormonal changes and metabolism

Sleep plays an important role in regulating hormones that control appetite, stress and energy balance. Lack of adequate sleep can increase stress hormones such as cortisol and disturb hormones linked to hunger and fullness.

As a result, people may experience increased cravings, irregular eating patterns and changes in metabolism. If sleep deprivation becomes a regular pattern, it may contribute to weight gain and increase the risk of metabolic conditions.

Impact on immunity and recovery

During sleep, the body carries out several repair and recovery processes. Deep sleep supports immune function, tissue repair and overall restoration.

Repeated sleep loss can weaken the body’s defence mechanisms, making a person more vulnerable to infections and slowing down recovery from physical and mental exhaustion.

Sleep deprivation can affect heart health and emotional wellbeing

Long periods of inadequate sleep can also affect cardiovascular health. Sleep deprivation may temporarily increase blood pressure, heart rate and stress on the body’s systems.

When poor sleep becomes frequent, it can contribute to higher long-term risks associated with heart health, especially in people who already have other risk factors. Sleep and mental health are also closely connected. Lack of sleep can make it harder for the brain to regulate emotions, leading to increased stress, low motivation, mood fluctuations and reduced ability to cope with daily challenges.

Chronic sleep deprivation may also worsen symptoms in people who are already experiencing anxiety or mood-related concerns.

Why recovery sleep matters

For people with demanding work schedules, maintaining a balance between professional commitments and adequate rest is important. Recovery cannot be replaced completely by occasional catch-up sleep, especially when sleep loss becomes frequent.

Maintaining consistent sleep timings, allowing sufficient breaks between work periods, eating balanced meals and recognising signs of excessive fatigue can help protect overall health.

Sleep is not merely a period of rest. It is an essential biological process that allows the brain and body to repair, regulate and prepare for the demands of the next day.