If you tell a therapist, hospital, police officer etc... that you are imminentaly suicidal (i.e. if oyu tell them you will do it in the next 24 hours or that you have a set date and a reasonable way to carry it out, or something to that effect) they are legaly obligated to have you detained for mental evaluation. Now, in no way am i trying to dissuade you from telling someone about it but i think you should first tell a friend or family member. someone who wont have the men in white knocking on your front door. because, forced incarceration can do a lot more harm then good (trust me i know all about incarceration and itd detrimental effects on the human psyche).