Each of us detects energies on subtle levels even if we don't at least initially recognize the significance. For example, whenever you sense a feeling in your gut to do something urgently or to avoid someone, these are ways you detect energy all around you. Your feelings and moods are symptoms or indications of certain kinds of energies and how you react to them. Consider the difference between how you react to positive, uplifting energies and how you're effected by draining energies.
