If you always wake up tired, it's time to look at the quality of your sleep.

You go to bed diligently at 11pm, setting your alarm for 7am the next morning. That's a solid eight hours of sleep, yet you still wake feeling as though you haven't slept in years. The grogginess and fatigue follow you throughout the day and all you can think of is climbing back into bed.

What gives? Here are five reasons why you might still feel tired after sleeping for seven or eight hours each night. Hint: quality matters.

1. You have sleep apnoea

Obstructive sleep apnoea is a condition where your airway becomes partially or completely blocked during sleep, causing you to briefly stop breathing throughout the night.

When this happens, your body becomes temporarily starved of oxygen and this can cause your brain to jolt awake so that you can breathe normally.

This disruption of sleep can happen so suddenly and quickly that you don't fully wake up or remember the episodes even if they occur multiple times a night.

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According to a study done by Jurong Health Services, one in three Singaporeans suffers from moderate to severe sleep apnoea and one in 10 suffers from severe sleep apnoea.

What's worse: sleep apnoea is a condition that is often under-diagnosed since many patients don't even know they have it.

Common symptoms of obstructive sleep apnoea include snoring, waking up with a headache in the morning, excessive daytime sleepiness, and insomnia.

Left untreated, sleep apnoea can lead to complications such as high blood pressure or heart problems. Speak to your doctor if you suspect you might be suffering from sleep apnoea.

2. You had a drink before sleeping

While alcohol may momentarily make you feel sleepy, it actually disrupts your sleep later on and may cause you to wake up prematurely.

According to the National Sleep Foundation in the US, your body's production of sleep-inducing adenosine in increased immediately after drinking. This can make you feel drowsy quickly, helping you to fall asleep faster.

But adenosine levels following alcohol drop just as quickly and may trigger you to wake up before you're truly well rested.

Alcohol is also said to block REM sleep, the stage at which your body undergoes repair and restoration, so you wake up feeling more tired.

3. You exercised too close to bedtime

The verdict's still out for this one as there isn't yet enough scientific evidence to prove the correlation between late-night exercise and disrupted sleep.

That said, it's also not surprising that anecdotally many people have said that it's harder to fall asleep if they exercise just before bedtime.

When you exercise, your adrenaline levels and heart rate increases, and this can make it more difficult to wind down and drift off to dreamland after. This is especially so if you're going hard with a HIIT routine or a fast-paced Zumba routine.

If you really don't have any other time to work out, try squeezing relaxing stretches or a gentle yoga flow before bedtime to calm your senses and slow your breathing and heart rate. This will promote more restful sleep throughout the night as well.

4. You had a cuppa during teatime

It's a no-brainer that caffeine affects your sleep, but it may be hard to estimate just when that 'cut-off point' is to avoid feeling the buzz before bedtime.

In a small-scale study published in the Journal of Clinical Sleep Medicine, researchers found that taking caffeine even six hours before bedtime resulted in significant sleep disturbances later at night.

Try avoiding coffee or tea beyond lunchtime so that your body has enough time to fully break down the caffeine before bed.

Watch out for caffeine in the less obvious suspects like colas, coffee-flavoured desserts and energy drinks.

5. You engaged in screen time just before bed

Do you have a habit of scrolling through your Instagram feed just before bed? Or worse, watching YouTube videos in the dark when you're already tucked in?

Bad news: your tech habits are seriously affecting your sleep quality. The blue light emitted by the screens on your computers, mobile phones, television and tablets all play a part in suppressing your body's natural production of melatonin, the hormone that regulates your sleep-wake cycles.

When this happens, your circadian rhythm is affected and it can be harder to fall into deep, restful sleep.

Try avoiding screen time an hour before bed and turning your phone to 'night mode' in the evenings so that your exposure to blue light is minimised.

This article was first published in Shape