You wont be hospitalized by just telling her about your dream. She will probably want to explore it to see if in your waking life you are having thoughts of killing yourself. A therapist or psychiatrist will hospitalize you if they think you are a danger to yourself or to others. The hospital is a safe place to be, and for me, it has saved me many many times from the anxiety of just trying to decide whether or not to kill myself. If it is something you are wrestling with intensely in your waking hours, it would be a good idea to talk to your therapist about checking yourself in.