A stuffy or congested nose occurs when the tissues lining it become swollen.
The swelling is due to inflamed blood vessels.
problem may also include nasal discharge or "runny nose."
If excess mucus runs down the back of your throat (postnasal drip), it may cause a cough or sore throat.
Nasal congestion can be caused by anything that irritates or inflames the nasal tissues. Infections such as colds, flu or sinusitis and allergies are frequent causes of nasal congestion and runny nose.
Sometimes a congested and runny nose can be caused by irritants such as tobacco smoke and car exhaust.
When you lie down, your blood pressure changes.
And blood flow to the upper part of your body can increase, including the blood flow to your head and nasal passageways.
This increased blood flow can inflame the vessels inside your nose and nasal passages, which can cause or worsen congestion.
If your nasal congestion is from a cold or flu, it will likely last as long your cold or flu (anywhere from five to 10 days) or even longer.
If your nasal congestion is the result of allergies, it may last longer, depending on your exposure to that particular allergen.