When you look up at the top of a stunning waterfall and catch yourself thinking, "That would be a good place to jump from".
When you're slicing bread and you realise how easy it would be to open your wrists.
When you take a walk along the waterfront on a stormy day, with the salty wind whipping your hair while the surf hurls itself against the seawall, and you idly wonder if they'd ever find your body.
When you're terrified to be left alone in the house in case of what you might do to yourself.
Don't be too afraid to ask for help.