Nasal congestion or "stuffy nose" occurs when nasal and adjacent tissues and blood vessels become swollen with excess fluid, causing a "stuffy" feeling. Nasal congestion may or may not be accompanied by a nasal discharge or "runny nose."

Nasal congestion usually is just an annoyance for older children and adults. But nasal congestion can be serious for children whose sleep is disturbed by their nasal congestion, or for infants, who might have a hard time feeding as a result.

A blocked nose or nasal congestion is when you wake up with catarrh dripping down the back of your throat, you find it difficult to breathe quietly, you are unable to exercise without struggling for breath and you feel as if you are always clearing your throat. 

Potential causes of nasal congestion include:

Acute sinusitis
Allergies
Chronic sinusitis
Churg-strauss syndrome
Common cold
Decongestant nasal spray overuse
Deviated septum
Drug addiction (substance use disorder)
Dry air
Enlarged adenoids
Foreign body in the nose
Hormonal changes
Influenza (flu)
Medications, such as high blood pressure drugs
Nasal polyps
Nonallergic rhinitis
Pregnancy
Respiratory syncytial virus (RSV)
Stress
Thyroid disorders
Tobacco smoke
Granulomatosis with polyangiitis (Wegener's granulomatosis)

Use a humidifier or vaporizer.
Take long showers or breathe in steam from a pot of warm (but not too hot) water.
Drink lots of fluids. This will thin out your mucus, which could help prevent blocked sinuses.
Use a nasal saline spray. It’s salt water, and it will help keep your nasal passages from drying out.
Try a neti pot, nasal irrigator, or bulb syringe. Use distilled, sterile water or H2O that’s been boiled to make up the irrigation solution. Rinse the irrigation device after each use and let it air dry.
Sit a warm, wet towel on your face. It may relieve discomfort and open your nasal passages.
Prop yourself up. At night, lie on a couple of pillows. Keeping your head elevated may make breathing more comfortable.
Avoid chlorinated pools. They can irritate your nasal passages.

https://www.mayoclinic.org
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