From page 29 of Man’s Search for Meaning. Frankl is writing about what role dreams played for concentration camp prisoners
I shall never forget how I was roused one night by the groans of a fellow prisoner, who threw himself about in his sleep, obviously having a horrible nightmare. Since I had always been especially sorry for people who suffered from fearful dreams or deliria, I wanted to wake the poor man. Suddenly I drew back the hand which was ready to shake him, frightened at the thing I was about to do. At that moment I became intensely conscious of the fact that no dream, no matter how horrible, could be as bad as the reality of the camp which surrounded us, and to which I was about to recall him.