Why do I bring this up? Because it affects the people around them, too. Negative energy can affect innocent bystanders. Especially people who are emotionally sensitive or in tune with their own internal energies.
Such was the case with me and two other friends who came home and that night and all during the next day - all three of us were sluggish, fuzzy-headed and exhausted. Even 5 days later I still don't feel not right. I have to concentrate to speak clearly. It's getting easier though.
So, if you know of a negative person, you may want to avoid them. Many people have relatives and people they care for who are negative. In those cases, protect yourself. Before you see them, picture a shell of positive energy around you, play music that makes you sing, appreciate the simple sights around you, enjoy your favorite coffee or other beverage. Build up the positive so that the negative can't get through. I wasn't prepared, sadly, and I'm still dealing with it days later.