Question
In the soil of one of my plants I've just notice mushrooms growing(this is in an INDOOR plant pot).  What does that mean?   Am I in any danger, is my air polluted, HOW CAN A FUNGUS JUST MAGICALLY APPEAR NEXT TO AN INDOOR PLANT??

Answer
Freddy,

Is this a new plant? Was the plant recently repotted? Have you brought any nearby new plants in? Yes your air is polluted with mushroom or toadstool spores, everyone's air is. Mold and fungus spores are microscopic and always float in the air, where the spores can land and grow depends on the conditions. Apparently those spores found the perfect conditions in your houseplant. That means you are keeping your houseplant too wet. It needs to dry out more between waterings and it will not support the growth of mushrooms. It also means the soil is very acidic to support the growth of mushrooms. You didn't mention what type of plant it is, it many need the acidic soil so that is fine but it does not need to be constantly wet so make sure the soil is dry on the surface and the pot feels some lighter before you water it again and the mushrooms will disappear, the plant will stay healthier and so will you. Good luck.

Darlene