Toads - you have to work quite hard to be hospitalised, and even harder to be admitted against your will.
Suicidal thoughts are really not uncommon, GPs and other MH professionals will not overreact to you saying you feel suicidal, but it is important that people know how you feel in order to get you the best help.
IME they work really hard to involve you in discussions about what you need - the scenario where people pile in and make choices for you against your will is really not the reality. They can break confidentiality, but again they will not IME do it behind your back or without discussing it with you. Obviously it will depend whether you are talking about having occasional intrusive thoughts about suicide but no specific plan, or whether you are actively suicidal and have access to means and the intention to carry it out.
Breaking confidentiality in practice should mean having a long discussion with you about how they need to keep you safe, making appointments for the crisis team to visit you at home, giving you PRN medication, phoning your GP to put a flag on your notes to ensure that you can get an apointment any time you need one, possibly asking to speak to other family members if appropriate to ensure that you're safe.
Reading other people's experiences I may have been lucky, but I would liken it to interventions in childbirth - you may not have started out wanting a ventouse or epidural or whatever, but there may come a point where you need these things, and as long as it's explained to you and you feel respected and consulted, it doesn't have to be an overwhelmingly bad experience.