This means putting herself in a near death state to see what she discovers. What she finds is this: a bright light, a long corridor, and a door. But it’s when she opens the door that she finds the real surprise. Joanna is on the Titanic, and the Titanic is sinking.
Joanna, to her horror, now knows that the distinction between death and near death is not at all as well-defined as her experiments have led her to believe.