We have all experienced different ways of waking up, or different moods let’s say, when we wake up. Sometimes we might sleep for more than 10 hours and still feel tired as if we had been running all night, and sometimes we wake up from a 15 minute nap and feel as good as new. Also, you must know that feeling when you wake up and feel lost in space and time and you need some time to get back to normal. You must have also woken up on your own before the alarm starts and decided to use that little time until the alarm starts for extra sleep. And after that it becomes extremely difficult to wake up. And sometimes, although very rarely at least for me, we wake up rested and in a great mood just like the people in commercials. So, why does this happen?
Besides the comfort of your bed or other external factors, there is this sleeping cycle that our bodies go through when we sleep. There are four phases in the sleeping cycle that are, however, not strictly separated from one another, but gradually change during the night.
sleeping cycle usually lasts around 90 minutes and repeats several times during the night.
The first phase is the transition between being awake and sleeping and lasts for about 10 minutes. In this phase there is slow eye movement, the muscles are still active but they start to relax and the heart rate begins to slow. You know, in the moments when you are very tired but you are trying not to fall asleep, after you blink there are two images overlapping when you open your eyes. This can happen along with a sensation of starting to fall and sudden muscle contractions. You can still hear and understand sounds and conversations, but you are most likely not going to respond to them. Usually, the person has the feeling being able, but not willing to do so. And if somebody wakes you up during this phase, you feel like you have not even fallen asleep at all. Well, according to this definition of sleep, you have! 🙂
After this period of very light sleep, the body gradually enters in the second phase, when we become less aware of the stimuli from the environment, the heart rate slows even more and since the muscles are less active the body temperature drops. Research shows that this is the longest phase and it is relatively easy to wake up from. So, for example, if you are cold, you might wake up, take a blanket and go back to sleep. You also might wake up if there is a louder noise or if somebody nudges you. This phase is not very restorative for the body, and we need the next two stages in order to get a good rest.
Next is the deep sleep phase, which it is the hardest to wake up from. We are mostly unaware of even stronger sounds and other stimuli. This is the phase when the body regenerates itself and strengthens the immune system. The blood pressure, heart rate, body temperature and muscle activity are at their lowest levels and the breathing is slow. If a person is awakened during this phase, they feel a little bit disoriented and have decreased cognitive capacity for a little while. In some experiments, people were awakened during different sleep stages and given some exercises that required mental activity. Results show that those awakened from the deep sleeping phase had lower performance than the ones awakened during the other stages. In rare cases, during this phase some signals from the brain cause awakening of the motor centers, but not the centers responsible for higher cognitive activities, so sleepwalking or sleep talking might happen without the person’s awareness.
The fourth stage, the REM phase (Rapid Eye Movement), is the phase where the wonderful world of the dreams takes place. It is characterized by random rapid eye movements, elevated heart rate, faster breathing and higher level of brain activity, while the muscles remain immobile. If you wake up during this phase you are most likely to remember the dream you had, or you might even wake up with the emotion connected to the dream. It starts about 70 – 90 minutes after falling asleep and is very important because it stimulates the brain, especially the regions involved in learning, thinking and organizing information. It makes us more energetic and more productive during the day. In the first half of the night the deep sleep stages last longer and then become shorter, whereas the REM stages become longer and might last up to an hour in the morning. This would explain why that 1 hour extra sleep in the morning makes such a big difference.
This sleeping cycle usually lasts around 90 minutes and repeats several times during the night. Knowing this, you can plan to wake up after a full cycle is completed. For example, if you can predict the time when you will fall asleep, you can plan waking up after 7,5 or 9 hours.
However, different kinds of factors, such as comfort, emotional state, alcohol, environmental conditions, circadian rhythm etc. can influence the sleeping cycle and the appearance, order and duration of each of the phases, thus influencing the overall quality of sleep. For example, if someone is awaken or unable to enter the third phase, they will experience very low quality of sleep and will be lacking the important benefits from it.