In Beginning to Pray, Met. Anthony Bloom gave this advice to a young person who had been praying for hours and hours at a time but felt that he couldn't bear to keep it up any longer:
"There are moments when you can tell God 'I simply must have a rest. I have no strength to be with you all of the time,' which is perfectly true. You are still not capible of bearing God's company of all the time. Well, say so. God knows that perfectly well, whatever you do about it. Go apart, say for a moment, 'I'll just have a rest. For the moment I accept to be less saintly.'"