[Epistemic status: Somewhat confident in the medical analysis, a little out of my depth discussing the statistics]
For years, we've been warning patients that their sleeping pills could kill them. How? In every way possible. People taking sleeping pills not only have higher all-cause mortality. They have higher mortality from every individual cause studied. Death from cancer? Higher. Death from heart disease? Higher. Death from lung disease? Higher. Death from car accidents? Higher. Death from suicide? Higher. Nobody's ever proven that sleeping pill users are more likely to get hit by meteors, but nobody's ever proven that they aren't.
In case this isn't scary enough, it only takes a few sleeping pills before your risk of death starts shooting up. Even if you take sleeping pills only a few nights per year, your chance of dying double or triple.
When these studies first came out, doctors were understandably skeptical. First, it seems suspicious that so few sleeping pills could have such a profound effect. Second, why would sleeping pills raise your risk of everything at once? Lung disease? Well, okay, sleeping pills can cause respiratory depression. Suicide? Well, okay, overdosing on sleeping pills is a popular suicide method. Car accidents? Well, sleeping pills can keep you groggy in the morning, and maybe you don't drive very well on your way to work. But cancer? Nobody has a good theory for this. Heart disease? Seems kind of weird. Also, there are lots of different kinds of sleeping pills with different biological mechanisms; why should they all cause these effects?