Just as there are parasites in the physical world that feed on impurities, there are also parasites in the subtle levels of nature, but you cannot see them with your physical eyes. These astral parasites are common where people think negatively, indulge in impure fantasy, or otherwise use their energies poorly. They are common in dirty places of any kind, such as where anyone fornicates, or garbage bins, dirty homes, movie theaters, bars, gyms and yoga studios (where lust is rampant), etc.
For instance, those who indulge in sexual fantasy and masturbation attract hordes of astral parasites to their environment, and also create very powerful parasites called incubi and succubi. Even if you have abandoned these activities, you still encounter people who have not.