It depends what the difference between "actively suicidal" and "passively suicidal" is. I'd bet that the vast majority of people who ctb have been suicidal for a long time. The biggest reasons that actively suicidal people don't ctb immediately are because they need a plan, they are scared to ctb, or they have obligations to stay. Many people ctb within a short time of a "crisis," probably because it overshadows the fear of dying. Some people are really at the edge of tolerating life that they are just waiting for one more excuse to leave. You can call it impulsive, but the reality is there is always a single straw that breaks the camel's back, so anyone can scrutinize that last straw and miss how it was always going to be arbitrary at that point.