Yes and no. Yes, they can feed off the negative energy of a person, but that arrangement is only viable so long as the person continues to invest energy in engaging with the chaos. One need only turn one’s attention to the positive or to turn one’s attention to the Self that observes the chaos or just disbelieve the importance of the chaos to cut any energy that a dark spirit might feed from.
It is literally monsters under the bed. They can only harass you to the extent that you buy in.