What does it mean when my tonsils swell up out of no where?

Tonsil hypertrophy: The tonsils are a first line of defense against incoming pathogens (germs) into the throat. As such they may swell in response to viral, bacterial and fungal or allergic entities. The swelling indicates the lymphocytes (white blood cells) in the tonsil are dividing and therefore the tonsil enlarges. If you are not having pus or pain, this may be a normal immune response.