By "that line", do you mean the border between life and death?

Fool! You were just on the verge of death!

People staring death in the face every day don't want to hear that someone's ready to die.

Get kinda anxious when my life's on the line.

In addition, I observed that today's dose of mutagens brought the subject to the brink of death. He then suddenly awoke, revived, his strength renewed. Not wholly, of course, but he did in a sense come back from the edge of death.