Apollo neurologist warns: Less than 4 hours of sleep can harm your brain and memory. What are the side effects?

If you’ve ever bragged about “running on four hours of sleep,” here’s a wake-up call. Dr Sudhir Kumar, a neurologist at Apollo Hospitals, shared on X that even one night of severe sleep deprivation can mess with your brain almost as much as mild alcohol intoxication. From slower reflexes to forgetfulness, the damage kicks in faster than you’d think — and it’s all backed by science.

Short term memory

According to Dr Kumar, sleeping less than four hours can significantly impact short-term memory. The parts of your brain that handle reasoning, decision-making, and recalling information — the prefrontal cortex and hippocampus — become sluggish. You might find it harder to follow conversations, remember new details, or even recall what you learned earlier in the day.

Attention span

Your attention span also takes a major hit. Lack of sleep triggers “microsleeps” — brief, uncontrollable lapses in focus that last just a few seconds but can have serious consequences. Reaction times slow down, multitasking becomes harder, and you’re more likely to make impulsive decisions or errors.

Driving after sleepless night

Dr Kumar also warned about the dangers of driving after a sleepless night. Research shows that operating a vehicle with less than four hours of rest is comparable to driving with a blood alcohol level of 0.08% — the legal limit for drunk driving in many countries. Sleep-deprived drivers are more prone to drifting between lanes, missing signals, or braking too late, often with no memory of the lapse due to microsleeps.


In short, even one night of poor sleep can throw your brain off balance — affecting memory, focus, and coordination just like alcohol would. If you’ve slept less than four hours, Dr Kumar advises avoiding driving or handling anything that needs sharp attention. Your brain, quite literally, isn’t in its best shape.