The reason why nasal congestion is worse at night is because when you lay down it increases blood flow to your head.
The increased blood flow to the head causes your nasal passages to swell up and potentially hinder mucus drainage which then leads to and causes a stuffy nose.
At night when you're laying down, the gravity causes more blood to flow to your head and including your nasal passages.
The increased blood flow can then cause blood vessels in your nasal passages to swell up and cause congestion.
Laying down also makes it harder for the mucus to drain naturally from your sinuses and your nasal passages which can lead to a buildup of the mucus and further congestion.
Also allergens and other irritants can accumulate in your bedroom and laying down can increase your risk of exposure to these triggers and exacerbate congestion.
Your body's natural 24 hour rhythm also can play a role in congestion as some immune cells become more active at night and can lead to increased inflammation and congestion.
Also dry air that can occur in bedrooms and other areas of the home can contribute to congestion as the dry air can irritate the nasal passages.
Using a humidifier in your home and bedroom at night can help ease congestion.
Other things you can do to help stop nasal congestion at night is to inhale some steam, take a steamy shower, use nasal sprays, take decongestants and keeping a humidifier going at night to increase moisture in your room.
Also when sleeping you should elevate your head to help relieve nasal congestion and unclog your sinuses.
Elevating your head with a few pillows can help your sinuses drain much more easily and some people even get relief from nasal congestion and stuffy noses when sleeping in a recliner or on a couch.