What does Frankl write happened to prisoners who lost hope in the future?

Frankl writes that those who lost faith in the future, who gave up, were in a dangerous position. He notes the case of a man who learned in a dream that he wold be free on March thirtieth. He fell ill on March twenty-ninth and died one day after he believed he would be free. Frankl also notes that around Christmas and New Years, when many prisoners had convinced themselves they would already be free, the death rate increased.