[Not_here]

Like the others have said they usually make a decision based on whether you're a danger to yourself or to others. Danger to yourself includes:
having a plan
having an intent to carry it out
having the materials required to carry out the plan or access to materials required to carry out the plan.

Also if you are badly injured as a result of Self Harm or overdose. Whether those were intentional for suicide or not, if a lot of damage is done you'd at least have to go to the emergency room to get you the medical care and if you told someone the paramedics would ask to see your arms and legs for any sign of self harm.
After that they might transfer you to the psychiatric unit. Until they find you can go home.
Well that's more or less what happened to me. At the hospital the stay is on average two weeks but can go up to months. The staff will keep an eye on you till they decide you can be discharged.
I know for myself I wouldn't want to go back to a hospital but really if you're this close to hurting yourself, I suggest to reach out to someone.
Even if they decide to take you to the hospital and you absolutely hate it there and find it unhelpful and time wasting, you may have a chance to gain some self discovery and you'll have a lot of time for reflection on how to improve your life for the better.
I wanted to ask if the environment you're in now is contributing to your suicidal. If you stayed over a friend's house, or relative for a while would that change your outlook on life?
Remember TH is here for you.