There are occasions when one cannot help doing this [i.e. suffer distraction]: times of ill-health (especially in persons who suffer from melancholia); or times when our heads are tired, and, however hard we try, we cannot concentrate; or times when, for their own good, God allows His servants for days on end to go through great storms. And, although they are distressed and strive to calm themselves, they are unable to do so and incapable of attending to what they are saying, however hard they try, nor can they fix their understanding on anything: they seem to be in a frenzy, so distraught are they.
The very suffering of anyone in this state will show her that she is not to blame, and she must not worry, for that only makes matters worse, nor must she weary herself by trying to put sense into something—namely, her mind—which for the moment is without any. She should pray as best she can: indeed, she need not pray at all, but may try to rest her spirit as though she were ill and busy herself with some other virtuous action. These directions are meant for persons who keep careful guard over themselves and know that they must not speak to God and to the world at the same time. What we can do ourselves is to try to be alone—and God grant that this may suffice, as I say, to make us realize in Whose presence we are and how the Lord answers our petitions. Do you suppose that, because we cannot hear Him, He is silent?
(from chapter 24. Text from Christian Classics Ethereal Library)