Mental health professionals have varied degrees of competence. You have a right to ensure your personal safety. Strange behavior is a symptom of the disorder. Don't take it personally. Don't be afraid to ask your sibling or parent if he or she is thinking about hurting him-or herself.
Suicide is real.
Don't shoulder the whole responsibility for your mentally disordered relative yourself. You are not a paid professional case worker. The needs of the ill person do not necessarily always come first. If you can't care for yourself, you can't care for another. It is important to have boundaries and to set clear limits.