For a while there I was getting 2-3 nosebleeds a day...can't tell me that isn't a sign that something is very, very wrong with the air.
Around here, that would mean the air is very dry. Though the area I live in is known for its humidity (and also hot air, but that's Congress), forced-air heat dries out the air in the house so much that both the kid and I have had nosebleeds because of it. When that happens, I run a humidifier, mister, or boil water on the stove to get some moisture into the air, and voila! No more nosebleeds, and the house feels warmer, too.