For some people that is true, either they don't need to touch in with the spirit anymore or they don't realize that the spirit is their around them. Ghost/spirits are around us almost all the time.
Its how open and aware you are to your own energies that you can pick up and feel or know that there is something different around you.
Yes, there are different forms of ghost/spirit, I view it like the break down as the seen light (ROYGBIV, red, orange, yellow, green, blue, indago, violet) It's not bad or good but different frequencies (sorry, I can spell without spell check
) Red has a different rate than violet. For the Poltergeists they would be a red area, and most humans are a yellow or higher, but we can go to the lower rates. Think of red as just basic living, hunt, mate kind of thinking and as you use your mind and expand your thoughts and energies you move yourself up the scale.
You can think of poltergeists as the red neck of the spirit world, those spirits love to stir things up. You can find them around people who open themselves up without control (legal/illegal drugs, drink or other) and/or place that had that around (bars, etc.). They also can be carried into a place as they pig back onto a person that is open without control. (with that I'd bet most gov. building, sorry a joke for me.)
That's why you need to protect yourself and clear the energies. Native Americans have sage, sweetgrass, and cedar, WICCA uses salt and other herbs around the house outside with blessing on the doors and window.
I didn't mean to write a book but I leave it with want works for one many not work for another, we're different energies that if we work together plus add in the other unseen things maybe it will be back the one white light as some say.