If you can nod off quickly, fall asleep deeply, fall asleep whenever you want, and fall asleep anywhere, you can consider yourself a perfect sleeper. But being able to fall asleep quickly can actually be a symptom of a sleep disorder.
This article explains the science of napping. It also talks about sleep disorders that cause daytime sleepiness.
How does drowsiness occur?
First, it is important to understand how we become sleepy.
When you are awake, your brain produces a chemical called adenosine. Adenosine accumulates when your body is expending energy and is normally awake. Adenosine levels gradually increase as we stay awake.
High levels of adenosine create what is known as the homeostatic sleep drive. This is sometimes called sleep strain or sleep debt. Simply put, your body needs sleep to restore itself. 1
For example, if you were awake for 30 hours straight, you would feel very sleepy. You would have fallen asleep easily and slept deeply. You may sleep longer than usual. This is because your brain has more adenosine.
Being late to your usual bedtime means you fall asleep faster because your adenosine levels are elevated.
When you sleep, your lymphatic system acts like a filter to clear adenosine from your brain. Adenosine levels and sleepiness are lowest when waking up in the morning. If you sleep well, you will feel refreshed.
But what if these levels are consistently too high?