What I've found with different therapists/psychiatrists is that the mention of suicidal ideation does not necessarily lead to hospitalization. In fact, I've gone as far as constantly thinking about suicide and having a plan without forced treatment. It was only when I'd mentioned that I'd taken steps (obtained a means of suicide, wrote notes, etc) that they were really alarmed.

I'm telling you this because I believe suicidal ideation is definitely something that should be told to your therapist. I've been burned before too and because of that have had to decide just how much of the truth to disclose in the future. But I just wanted to let you know that the mere mention of suicidal thoughts does not automatically guarantee hospitalization, especially if such thoughts are rather normal for you.