Fibreglass insulation has microscopically small bits of glass that are free to blow into the air. When house drafts pull it into the air you will inhale them. They cut their way through your lungs and organs like millions of tiny knives, spreading through your body, since there is no way out for them. You smell nothing and feel nothing. This makes it a very sinister poison. Your body, though, recognizes these sharp, pointed bits and tries to stop their spread by sequestering them in cysts.
Most solid malignant tumours contain fibreglass or asbestos, another glass-like particle. In nearly all cases a hole can be found in the ceiling or walls, leading to fibreglass insulated parts of the house. When these holes are sealed in an air-tight manner the house air no longer is positive for fibreglass. Covering with panelling is not sufficient. Check your dwelling for uncovered fibreglass. Repair immediately. Search for small screw holes intended for pictures, or electric outlet plates that are missing.
Also remove fibreglass jackets from water heater and fibreglass filter from furnace. Replace with foam or carbon. Best of all, hire a crew to remove it all from your home, and replace insulation with blown-in shredded paper or other innocuous substance.
Never build a new house using fibreglass for any purpose.