Albert Barnes Commentary John 11:12

"The disciples therefore said unto him, Lord, if he is fallen asleep, he will recover." — John 11:12 (ASV)

If he sleep, he shall do well. Sleep was regarded by the Jews, in sickness, as a favourable symptom; therefore, it was said among them, "Sleep in sickness is a sign of recovery, because it shows that the violence of the disease has abated" (Lightfoot). This seems to have been the meaning of the disciples. They intimated that if he had this symptom, there was no need of his going into Judea to restore him.