Something similar happened to me in late 2019. I couldn't stop thinking about killing myself. The idea was in my head nonstop, my brain conjuring up ways on how I'd do it.. it reached to the point where it started to scare me because I genuinely believed I was gonna pick up that knife in the drawer and slash my wrists. I panicked and rushed to the school because it was the only place I knew at the time where a counselor was available. I tried to stay calm but when one of them asked, "How can we help you?" I broke down and told them I needed help. The counselor who spoke to me admitted that she contemplated putting me on a 72 hour psych hold to make sure I wouldn't hurt myself. She decided against it and thought maybe she could try to talk to me first. I will never forget that feeling. Like you said, that impulse, the urgency to end it all..