Is it serious if x-rays show the nasal sinus cavities completely opaque and i have very thick almost glue-like mucous that is hard to blow out?

Will need antibiotic: Sounds like you have a sinus infection which will need antibiotics for treatment. Sometimes steroids can help as well with symptoms.

Glue-like nasal mucu: It is not serious that the x-rays show complete opacification. This finding is not specific for diagnosis of a sinus infection. Primary therapy should focus on alleviating nasal inflammation and thinning and improving mucus flow. This includes a mucus thinner like guafenasin, saline nasal rinses, increasing hydration and use a nasal steroid like flonase. Managing allergy symptoms is critical.

No Not Now But...: Dr. Anifat balogun has given you a good answer, and the fact is that you have noted a potential problem that is not bothering you now. But it may, and it is a potential source of future complications. I recommend hot showers, using a humidifier where you sleep, and getting in the habit of sleeping with your head horizontal first left side, then right so that the sinuses can drain properly. Neil mcleod dds dentistry that lasts - quality that counts.

ENT consult: Go to your ENT for a definitive diagnosis and possible antibiotic therapy if needed.