Sleep, like breathing, isn’t something we think much about until it goes wrong. You will have realised that this site is dedicated to helping you get back to the restful and restorative sleep you’re used to. In this article we’re going to answer questions that people often ask in relation to sleep.
We’ll look at:
- How much sleep do I need?
- What is sleep debt?
- What is sleep latency?
- What are the stages of sleep?
- What is REM sleep?
- What does a sleep study show?
- What are circadian rhythms?
- Why do I talk in my sleep?
- What are circadian rhythm disorders?
How much sleep do I need?
Individual needs vary and we need more at some times in our lives than at others. Babies sleep 16-18 hours a day, pre-schoolers need 11-12 hours and school-aged children through to teens need about 10 hours’ sleep. On the whole though, it’s recommended that adults sleep for 7.5 to 8 hours each night.
Some people can sleep for less time and stay healthy and are able to function well. Former British Prime Minister Margaret Thatcher said she only needed 4 hours’ sleep. This is extreme.
Remember that it’s not just the quantity of sleep you get, but its quality that will help you feel refreshed in the morning. See below in ‘Stages of Sleep’ for more on this.
Experts are not agreed whether older people need less sleep than younger adults – some studies say they don’t and others disagree. Sleep problems can come from medications you’re taking, sleep apnea, anxiety, restless leg syndrome and other sleep problems and lack of sleep can lead to memory problems, daytime sleepiness and over use of sleeping meds.
There is some evidence, however, that as we age our biological clocks (see below) alter slightly and that we need to go to sleep earlier and then wake up earlier.
What is sleep debt?
If you don’t get enough sleep over a long period of time (and this will vary for every individual) you build up a sleep debt. This is like any other debt – being overdrawn at the bank for example – and your body will demand that it’s repaid.
Sleep debt will affect your physical health (possibly even shortening your life span), emotional state, mental health and your relationships. Missing a few hours’ sleep over a few nights, such during a busy party season around Christmas, can be put right with a few extra naps or extra hours at night but chronic insomnia will take a toll on your health.
What is sleep latency?
Sleep onset latency is the time between switching the light off and getting to sleep. The average time is about 15 minutes.
Sleep latency is also a term used to refer to the time it takes you to fall asleep and reach Stage 4 sleep and then Stage 5 REM sleep.
What are the stages of sleep?
Once you’re asleep you go through 5 stages of sleep. Dreaming usually occurs in REM (Rapid Eye Movement) sleep and Non-REM and REM sleep occurs in cycles – called ‘sleep cycles’. The nature of these cycles (sleep scientists call this ‘sleep architecture’) will dictate the quality of your sleep and your health. Stages 1-4 are Non-REM stages.
Stage 1 sleep is a light sleep during which you can easily be awakened. You muscles are relaxed but twitch occasionally and your eye movements are slow. If you watch someone sleeping at this stage you’ll see the eyes moving gently backwards and forwards under the eyelids. This stage makes up about 5% of your sleeping time.
Stage 2 is still fairly light sleep. Eye movement stops and brainwaves are generally slower but with short bursts of rapid activity. Your total sleeping time comprises about 50-60% of Stage 2 sleep.
Stages 1 and 2 are fairly quick and you get to Stages 3 and 4 sleep in the first half of the night.
At Stages 3 and 4, sleep becomes increasingly deeper, muscles are still relaxed and your heart rate and breathing rate are slow. This deep sleep means it’s often difficult to wake the sleeper at this stage. It’s called ‘slow wave sleep’ and accounts for about 20% of your time asleep.
Stage 4 sleep is most important in helping you to feel refreshed when you wake. If it’s shortened or missing then this could be one reason why you still feel tired after a long night’s sleep.
Stage 5 is when REM sleep happens about an hour and a half after your calls asleep and at this time your heart rate, breathing and blood pressure become irregular. Your muscles are paralysed.
What is REM sleep?
During REM sleep the eyes move rapidly under the eyelids.
It is dreaming sleep although no one really knows why we dream and why this type of sleep is so important to us. It is thought that the brain is sorting information, making sense of it and laying it down in our memories. While doing this it plays scenes randomly and mixes them up which is why dreams seem so odd when we’re awake.
Interestingly, sleep scientists have found that if REM sleep is disrupted on one night REM sleep time will be longer on the nights following so that you catch up.
Find out about REM Sleep Behaviour Disorder here.
What does a sleep study show?
The medical term for a sleep study is a polysomnogram.
When you’ve had a sleep study done at a sleep lab, a long and detailed report is produced. It’s made up of the readings from the machines measuring your brain waves, respiratory rate, blood pressure and heart rate among other things.
This can be 100s of pages long and your clinician will summarise it. There are several readings that will help your doctor make sense of what’s happening and not happening. We’ll look at a few of these here.
- Total Sleep Time (TST) looks at the amount of time you sleep, based on brain wave readings. Sometimes you feel that you’ve hardly slept at all but you have actually slept for several hours. The electrode readings can confirm or deny this perception.
- Sleep Efficiency is the ratio between the time the electrodes were actually recording and the time you spent asleep. If you have difficulty getting to sleep or staying asleep your sleep efficiency is said to be compromised. This is common in conditions like depression.
- Sleep Onset Latency is the time between switching the light off and getting to sleep. The average time is about 15 minutes.
- The arousals or awakenings that happen during the night that you don’t remember can affect the quality of your sleep. In sleep apnea you wake many times in the night and can spend too little time in the right stages of sleep (see above) so that you wake feeling as tired as when you went to sleep.
- Cameras are often filming you as you sleep, so any abnormal activity (such as REM Sleep Behaviour Disorder, sleep walking or sleep talking etc) can be monitored.
Information for this section from Georgetown University and the American Academy of Sleep Medicine Task Force.
What are circadian rhythms?
Circadian rhythms are the changes we experience during a 24 hour cycle of our lives. They include physical, mental and behavioural changes and are a response to light and dark cycles in our environment.
Our biological clocks drive our circadian rhythms and these biological clocks are groups of cells throughout the body. They interact with one another and are coordinated by a ‘master clock’ in the brain.
This master clock is a group of 20,000 nerve cells called the suprachiasmatic (say sooprah-ky-yaz-mattik’) nucleus – SCN for short. It is situated in an area of the brain near the eye nerves, called the hypothalamus and controls the release of melatonin, the hormone that makes you sleepy.
- Circadian rhythms influence sleep-wake cycles, hormones and body temperature.
- They can be genetically influenced, so if you have a relative with circadian rhythm disorder then you may inherit this tendency.
- Abnormal circadian rhythms are linked to depression, bi-polar disorder (manic-depression) and seasonal affective disorder (SAD), jetlag and shift working sleep problems.
Why do I talk in my sleep?
The medical name for sleep talking in somniloquy (say “somm’nill-o-kwee”).
Talking out load in your sleep can occur at any stage of REM or Non-REM sleep (see above ‘Stages of Sleep’) and it’s very common. More than 50% of young children talk in their sleep at some stage, and about 5% of adults.
- What’s said often seems like nonsense to the listener or may not be understandable.
- It may also be offensive or rude.
- It can disturb a bed partner or roommate if it’s loud.
- It can occur as part of another sleep disorder, medical condition, a medication the sleeper is taking, mental health problem or as part of substance (alcohol, controlled drug) abuse.
- It’s often harmless and doesn’t need treatment. A sleep specialist will help if necessary.
What are circadian rhythm disorders?
These are sleeping problems where there is a mismatch between the body’s circadian rhythms and its sleep-wake cycles. This might happen because of travelling (jet lag) or shift working for example.
With a circadian rhythm disorder you’re awake when you should be sleeping and feeling sleepy when you should be wakeful.