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Why I feel tired even after 8 hours of sleep?

Do you often go through the day feeling sleepy and lethargic, even after 8 hours of  night rest? While it’s common to occasionally feel tired during the day, persistent symptoms of daytime drowsiness could be linked to your sleep habits, lack of knowledge of sleep cycle.

Sleep is very essential for life. In 1980s, scientist form university of Chicago conducted a study in rats. They design the experiment where the rats are deprived from the sleep for many days. Within a week sleep deprived rats started to lose weight and their fur began to fall. Despite having access to food they were not eating much. After a month, all of them died. Therefore sleep is very important for well-being. Even a minor reduction in the sleep can increase the chance of having serious accident in life.

Firstly, you should know basic knowledge about sleep cycle. There are two types of sleep; REM (Rapid eye movement) and NREM (Non-rapid eye movement, it includes four stage 1-4).  Light sleep is stage 1, 2 where as deep sleep is stage 3, 4 of NREM. There will be the sleep cycle of about 90 min, transition from NREM stage 1,2,3,4 then to REM sleep. REM sleep last for 10 min in the initial phase of sleep. In the morning time REM sleep dominates than other types of sleep. The sleep cycle is repeated usually four to five cycles at night.

Dreams mostly occur in REM sleep. We will wake up with biological clock in morning after REM sleep that is at stage 1,2 of sleep cycle. In the morning, if you wake up after completing the REM sleep, then you will feel fresh but if someone wake up in  REM or deep sleep then might feel drowsiness.

In other words, if we were to sleep naturally, without alarm clock or other sleep disturbances, we would wake up on the average after end of multiple 90 minutes sleep cycle. This means that you will feel most refreshed when you awake at the end of a 90-minute sleep cycle because you will be closest to your normal waking state. Let’s imagine that you want to wake at 6 am and wish to go to sleep around midnight.

Counting back in 90-minute segments from 6 am would look like this:
6 am>4.30>3.00>1.30>12:00>10.30 pm

So, to complete 5 sleep cycle you have to sleep around 10:30 pm, you can now plan yourself according to wake up time when to sleep to get complete sleep and feel refresh.

Seven and half hours is a good benchmark because the average person goes through five 90 minute sleep cycles alternating between sleep (non-REM) and REM sleep. Try this 7.5 hours sleep duration  and make habit of sleeping and waking time at same time to become fully energetic in the morning.

Moreover, there are other factors also that cause tiredness in the morning like snoring, sleep apnea, mattress quality, using sedative drugs, antiallergic drugs, and so on.

Dr. Sanjay Maharjan, MD
Dr. Sanjay Maharjan, MD
MD in Basic and Clinical Physiology


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