When you nose quits breathing well (primary symptom) and when this comes on suddenly it is most likely either a viral infection or an acute allergy flare up. Here are a few clues that might help you decide, and knowing what you have helps know what to expect and how to treat. 

Viral Infection Clues 

If you have been around young children or people who are sick (have the crud), then a viral infection is most likely. Viral infections can differ from illness to illness, so you can't always assume that you know what it feels like. There are hundreds of different viruses and they can have different presentations. 

Viral infections often start in one place, (one side of nose, throat, chest) and then over the course of one or two days spread to the rest of the upper airway. People often produce large amounts of initially clear nasal mucous. 

When in doubt, it is safest to assume that an acute onset of nasal obstruction is from a viral infection. You should assume that you are contagious and wash your hands frequently to reduce that chance of spreading the virus.

Especially when there is some possibility that it is allergic, I would usually treat it as if it is viral but consider adding antihistamines into the treatment plan.

Acute Allergic and Non-Allergic Rhinitis Clues

If you have had some obvious exposure to allergens, then an acute allergy flare up is possible. An acute case of non-allergic rhinitis is also possible. The symptoms are generally short lived once the exposure is eliminated.

Common non-allergic rhinitis exposures 
Perfumes, solvent fumes, smoke, dust 

Allergic and non-allergic rhinitis often has a history of previous similar experiences that are also short lived. Sneezing, itchy red eyes, lack of sore throat, and lack of cough are clues that such an exposure may be to blame. If you do not get this type of airway obstruction frequently and if there is no obvious exposure to some irritant, then allergic and non-allergic rhinitis is not likely the cause.

For patients with frequent airway blockage, several things come to mind: Chronic sinusitis, perennial allergies, primary turbinate hypertrophy, and anatomic abnormalities.

It can be difficult to determine just what the problem is from this symptom. Often the physical exam is helpful in narrowing down possibilities.

If you also have sinus pain or headaches, this points to a chronic infection
If you also have sneezing, itchy eyes, and seasonal flare ups, allergies are likely
If you have asthma or aspirin allergy, then nasal polyps are more likely
If you have ever had a nasal injury, then a nasal septal deviation is more possible


You can start out by treating your problems like as noted in The OTC treatment for chronic problems section and if the problem doesn't improve, a visit to a specialist is warranted.

When one side is primarily affected, then a couple of problems are much less likely. For example, it would be uncommon for allergies to affect primarily one side. Nasal septal deviations are a more likely diagnosis when one sided airway obstruction is the primary problem.

Unfortunately, chronic infections and nasal polyps can affect just one side, in fact they often do. With one sided obstruction, a physical exam by a specialist can usually provide a diagnosis. Treatment as noted in the section The OTC treatment for chronic problems section is a reasonable starting point for this symptom complex. 

Trouble breathing when you lay down is an especially common complaint. It is somewhat nonspecific. The usual story is that once you lay down, your nose becomes congested. Often the "downhill" side is worse and if you roll over, the sides switch and one opens back up, the other closes off.

The mechanical reason is that your turbinates are the structure that can change size most dramatically to effect your nasal airway. They are filled with blood vessels that can change tone and caliber. When you are up and about, your head is sort of "propped up". It's like propping up you ankle if its swollen, well, your head is propped up all day. When you place it low, in line with your heart, the relative venous blood pressure increases and the vessels can become engorged. Even the difference in elevation caused by the high side verses the low side when laying on your side can have an effect.

This effect is often in addition to other nasal problems and makes them become symptomatic only at this time for some people.

Another possible explanation for nighttime nasal airway obstruction is that you may be allergic to dust mites. If so, there is often a large quantity in you bedding. This has nothing to do with cleanliness. If this is suspect, you can purchase mattress and pillow covers that keep the antigen in the mattress and pillow and away from your nose. Quarantine is the only answer, you cant eradicate dust mites.

I usually recommend using a steroid nasal spray before bed. This can help either and both of these possibilities. You should try this for at least a week before drawing a conclusion. If this has not helped the problem, and if it is long standing, a visit to a specialist is in order. At times a simple in office procedure, (one of the submural turbinate reduction techniques), can relieve this symptom and can greatly aid sleeping. Breathing through your nose better can also help some snorers.

When one side is primarily affected, then a couple of problems are much less likely. For example, it would be uncommon for allergies to affect primarily one side. Nasal septal deviations are a more likely diagnosis when one sided airway obstruction is the primary problem.

Unfortunately, chronic infections and nasal polyps can affect just one side, in fact they often do. With one sided obstruction, a physical exam by a specialist can usually provide a diagnosis. Treatment as noted in the section The OTC treatment for chronic problems section is a reasonable starting point for this symptom complex.