Yes, I've been. Three and a half week involuntarily and I ended up staying another week voluntarily.
I think that if you're suicidal and want to be admitted to a hospital you're not really suicidal - or not THAT suicidal - because if you want to be admitted and thus have the chances of you commiting suicide reduced, you don't truly want to die, do you?
I still want to die but I'm immortal so regrettably that's not going to happen.