Is sphenoid sinus infection dangerous should I be very worried it?

It can be dangerous. Would see a physician asap. Appropriate antibiotic therapy should be initiated.
Depends. It depends what is causing it. Viral infections are fairly common and mild, requiring only supportive care. A bacterial infection, you may need to take antibiotics for to clear and prevent from spreading. A fungal infection, like mucormycosis, is life threatening and needs surgery immediately.