My character, Thabisa, has seen strange nightmares ever since she was a child, that could never be explained. Now they have been explained via combination of science and magic, and the reason is going to be a new weakness for her.
Nightmare: Thabisa's subconscious is occupied by a creature of darkness, a Nightmare, that causes her to have very vivid bad dreams every time she sleeps. In the dreams Thabisa is completely lucid and can feel emotions and sensations, sometimes even pain, but has no control over the dream itself. The Nightmare feeds on the negative emotions these bad dreams cause. The feeding has no effect on Thabisa, and the Nightmare doesn't feed on any negative emotions that aren't caused by the bad dreams it creates.
Nightmare: Thabisa's subconscious is occupied by a creature of darkness, a Nightmare, that causes her to have very vivid bad dreams every time she sleeps. In the dreams Thabisa is completely lucid and can feel emotions and sensations, sometimes even pain, but has no control over the dream itself. The Nightmare feeds on the negative emotions these bad dreams cause. The feeding has no effect on Thabisa, and the Nightmare doesn't feed on any negative emotions that aren't caused by the bad dreams it creates.