Hello and thank you for using HCM. I carefully read your question and i totally understand your concern. I will try to explain you something and give you my advise. As you clearly explain your cousin is having nightmares of killing her self, having ideas and voices for killing her self. This are clear singes of a stress disorder, anxiety or a neurotic problem. Stress disorders, anxiety does cause heart palpitations, dizziness, fast heart beats. All these together might cause difficulties in breathing deeply. This electrical heart issues, fast heart beats, palpitations might have different causes where stress is the most important one. Caffeine products,alcohol, energy drinks can rise heart frequencies so it mandatory to avoid them during this time. So, as we are dealing with a very young person my opinion is that we are in front of a stress disorder or a neurotic problem. I will strongly recommend you to help your cousin to meat a neurologist or a psychiatrist and talk about this problem, the nightmares, the killing ideas ect. Treating in time this problem will also resolve the heartbeats and other symptoms. There are a lot of remedies for stress disorders or anxiety with just therapist or with medications.It is just necessary to act in time. Hope I was helpful. Wish your cousin good health. Best regards.