To me it meant dwelling on something bad, and basically refusing to move on. Sure if something horrible happens it's... horrible, but never letting go isn't healthy.
Good moods are contagious, as are bad moods. People generally like to be around happy people too. But if someone you really care about was always sad... you'd either become sad too or get fed up and move on without them.
To smother someone with positivity? Well, that seems like it wouldn't be so bad... there isn't any real reason I can think of to try not to be happy and spread happiness to others. "smother" would be a bad way to describe that though, maybe "shower".
Hope that helps.
