This excerpt originally appeared in the novel "Lying Awake." For online information about this title or other books from Random House, please visit their website.

Two squirrels raced down the trunk of the sycamore tree and halted on a branch. They twitched their tails without looking directly at each other, then spiraled back up into the canopy.

I made a commitment to live by faith, not by reason.

The ever-changing pattern of jet trails overhead was the only visible reminder that the cloister occupied a specified place and time in the world.

Leaves against the sky. Green for Ordinary time, blue for the Marian feasts. The Blessed Virgin's mantle of compassion embracing the world. Sister John had promised to announce the results of her medical tests to the community following the Mass of Our Lady of Sorrows. She had several days until then to meditate and pray on the news in private, and to decide what to do.

I felt so empty for so long, Lord, but I did not turn my back on you. I gave up everything to search for you, and when I had lost everything, you found me. How could I ever doubt you?

From the materials the doctor had given her, she learned that temporal-lobe epilepsy sometimes caused changes in behavior and thinking even when the patient was not having seizures. These changes included hypergraphia (voluminous writing), an intensification but also a narrowing of emotional response, and an obsessive interest in religion and philosophy. The novelist Dostoevsky, who was epileptic, followed this model so closely that the syndrome was eventually named after him.

"There are moments," Dostoevsky wrote, "and it is only a matter of five or six seconds, when you feel the presence of the eternal harmony...a terrible thing is the frightful clearness with which it manifests itself and the rapture with which it fills you. If this state were to last more than five seconds, the soul could not endure it and would have to disappear. During these five seconds I live a whole human existence, and for that I would give my whole life and not think that I was paying too dearly...."

The similarity to her own experiences was unmistakable. If Dostoevsky had been given the option of treatment, she wondered, would he have taken it? Should

he have?

The article went on to speculate that other gifted artists and writers may have suffered from the disorder. Van Gogh, Tennyson, and Proust were mentioned as likely candidates, along with Socrates, Saint Paul, and Saint Teresa of Avila.

Saint Teresa's seizures--along with her heart attacks, chronic nausea, and even a three-day coma--were a matter of Church record. No one agonized more than she over the question of how to tell the difference between genuine spiritual experiences and false ones. At one point she even feared for her own sanity, but after being assured by Saint Peter of Alcantara that her spiritual favors were from God, she never again lost confidence in her visions, even after being denounced to the Inquisition.

Teresa called illness her greatest teacher, but she also warned against seeking illness as a means of cultivating holiness. She saw doctors for her maladies; when she wrote about turning suffering into opportunities for grace, she was almost certainly talking about incurable illness. She exhorted her readers to stay as healthy as possible so that they could all serve God to the best of their abilities.

But if looking after the body was so important, Sister John wondered, why hadn't Christ answered Pilate's questions and spared himself execution? Wasn't the point of his sacrifice to inspire the rest of us to place faith before self-concern?

If what you have shown me these past three years has all been a mirage, then I am worse off now than I ever was. If I lose my sense of you, I lose everything.