On the other hand, drugs with drowsiness as a side-effect (eg certain types of analgesia, antidepressants) are best administered in the evening so that patients can sleep off the effect and be alert the following day.
If you sleep off the effects of too much travelling, drink, or food, you recover from it by sleeping. It's a good idea to spend the first night of your holiday sleeping off the jet lag They had been up all night and were sleeping it off