well since you ask (ha ha)... you can be held as a volunatary or involuntary patient here in canada... more info than you ever wanted at
http://www.qsos.ca/mha.html. if you are voluntary you can leave at any time and cannot be restrained. i've been both voluntary as well as on a form (involuntary).
the important part in being involuntary, or on a form as it's called, is this section of the mental health act:
# "apparently" has a mental disorder "of a nature or quality" that will likely result in: a) serious bodily harm to self, or b) to others; or c) serious physical impairment of the person, and the person:
# threatens or has threatened to cause bodily harm to self
# attempts or has attempted to cause bodily harm to self
# behaves or has behaved violently towards someone else
# causes or has caused someone to fear bodily harm,
# shows or has shown a lack of competence to care for self.
initial holds are 72 hours. then if they want to extend it they can for another two weeks.
when they interview you they want to know how serious your attempt was / intent is ... if you answer that you are serious about making another attempt you will be held on a form. if you made an attempt but say you will not reattempt they will encourage you to admit yourself on a voluntary basis.
they don't usually admit for self-harm, even if it is serious, at least at the hospital i attend. they are well versed in the difference between self harm and suicide.
admissions are covered under provincial health insurance, if you have it. when i first moved back i didn't have health insurance (takes 3 months to become eligible). i had to pay for my hospital stay. it was $1000 a day. they gave me lots of time to pay it back, though, so it was okay.