I think there's usually a suicide attempt before, and often there's suffering for a period before someone attempts. Sometimes, if there's alcohol involved, there can be impulsive events. The strongest evidence around suicide prevention is around restricting lethal means—for example, access to firearms like hunting rifles, and access to large quantities of medications. Those are two, really, that have been shown to have quite a bit of evidence.
I think most people suffer for a long time, but if there is alcohol involved, sometimes it's quite impulsive when that event occurs.