Muscles relax during sleep, including those in the face.
The
nervous system relaxes
when we go into a deep sleep, which can also cause our facial muscles to relax. This can lead to our mouths
falling open and drool escaping from the sides of our mouths.
Also saliva can spill out of your mouth as drool when your facial muscles relax in your sleep like if the mouth
falls open. Since the muscles around your mouth are relaxed, your mouth can be relaxed enough that saliva
slips out.
Once in sleep cycle, your body’s muscles, including those in your face and mouth, start to relax, often resulting in
less swallowing and more drool.
But sometimes when you're asleep, your brain forgets to tell your throat and mouth muscles to swallow, causing
saliva to commute from your mouth to your pillow.
As you sleep, your body enters a state of relaxation and restoration. This means that your muscles relax –
including all of the muscles and tissues in the airway.
When these tissues relax, they may fall back into the airway, partially blocking your ability to breathe normally.
Sometimes causes your throat to compress as your tongue falls further back into your airway and the open
space behind your tongue and soft palate is reduced.
Inhaled air becomes turbulent. Directly inhaled air vibrates the soft tissues at the back of your mouth
Though breathing is an involuntary function and it may be difficult to control how your breathe while sleeping, if
you sleep on your side, the saliva collects in the side of your mouth and the reflex does not kick in to get rid of
the drool. However, if you sleep on your back, saliva collects in the back of the throat and leads to automatic
swallowing action.
If you breathe through partially blocked nose, greater suction forces are created that can cause your throat to
collapse and bring on snoring where your uvula and soft palate start to flap.
When we fall asleep, many muscles in our body relax. This is true of the muscles in our airway, since not fully
conscious. When you doze off and progress from a light sleep to a deep sleep, the muscles in the roof of your
mouth (soft palate), tongue and/or throat relax more.
This usually happens when the muscles in your body (including your face) relax during sleep, especially during
your REM cycle. When this happens, your jaw falls slack and your mouth falls open.