Lie down on your side with the clogged nostril higher than your clear nostril. Breathe normally and you'll notice your nostril will unclog after a few minutes, works 90% of the time.
Think of the clog as a mass behind your nose and gravity is shifting it to the middle. FYI it might switch to the other nostril, so it might take a few attempts before you clear both and at the very least you get a bit of easy relief without meds or more aggressive methods.
Supposedly it has nothing to do with gravity. It's a physiological reaction to pressure on your armpit. Supposedly you can induce it in any position. Put pressure on your right armpit and your left nostril will clear. I've never tried it.
Do not listen to medical advise on a public forum. Most advice will not help and some may actually be harmful.
Ask a doctor or at least pharmacist.
My current understanding (as an engineer not a medical person) is that the human body shrinks one nose side itentionally. This way you have a wide nose way and a narrow one. This leads to different airspeed which lets you smell different stuff better. The body changes sides in intervals. One allergic reaction is that the interior of the nose swells more. So the narrow path will become even narrower until it blocks.
There are substances that combat this swelling, but using them for too long can severely damage your sense of smell and health.
I had issues with my nose for ages and got the tip to use a Rhino Horn from a friend. Using it daily helps a lot, but still one passage gets clogged up regularly. This is a cheap way to clear the passages, as all you need is water and kitchen salt. (later I discovered I have hay fever... ah well, this works better then any medication.
I use a version of this, it's based on the neti pot from india. Completely natural technique and does more than clearing our your sinus. It also stops any post nasal drip, Globus (lump in the throat) and can help with snoring.
You have to get this from the pharmacist counter and show ID.
The government replaced pseudoephederine (how Sudafed got its name) with phenylephrine as the easy access decongestant. It has had multiple studies done that show it is about as effective as a placebo.
Every situation is different so it is best to check with your doctor.
For me the surgery was quick, I didn't even feel any difference when I woke up from the anaesthesia. I was released from the hospital within the same day. I rested at home for a few days, had to avoid lifting heaving stuff or sports for a few weeks.
Now I can breathe without having to open my mouth all the time.
I don't know why this works or if it will work for you, but it works for me like 95% of the time when I have a mild cold or something. Breathe through your nose as slow as you possibly can. That's it. Obviously don't pass out so if you feel you have to, then take a few normal breaths. It helps if you're calm and your heart rate slows down.
I used to get addicted to nasal sprays all the time and haven't used one since I found this method.
Hold your ear on the blocked side about level with the ear canal and pull out wards, the place your opposite thumb on at the bone under your eye and next to your nose and push in the same direction. Should open things up.