It's true that no one literally sleeps all the time, so the statement is fundamentally false, but the person saying it is not trying to tell a falsehood; he is using an exaggeration to emphasize a point.
If someone tells their doctor that they sleep all the time, they are really saying that they feel tired much of the time, and they sleep more than they usually do. For example, they might be taking a mid-day nap, which they never used to do. This is an important clue for the doctor, because a sudden change in sleeping habits, along with extreme fatigue, can be the indication of a medical problem.
- For Teachers