I recently had a really rotten experience with a volunteer in-patient program. I, like you, vowed I would never do that again. Still, you need to be able to talk the mental health professional you are trusting with your care. May be try putting it in more abstract terms. You know...not about something that is happening right now, but as a hypothetical you want to propose to better clarify your treatment relationship. If it was me, I might say:

"Listen...I had a REALLY awful experience in the past with confiding in my psychiatrist with regard to suicidal ideation. I need to know that I can talk to you about IDEATION and have you understand that it is distinct and separate from INTENT. If I begin to have INTENT, I will tell you, but I also need to know that I can discuss the ideations without you flying into a panic and hospitalizing me. If I can't discuss these ideations freely, without fear of unnecessary, involuntary hospitalization, then I'm going to have to find somebody else who I CAN discuss these things with."

Does that help?