how come my sulcata tortoise is not eating but sleeping all day long?

I have two Sulcata Tortoises and they sleep all time. Sometimes i have to poke at them just to see if they are alive! Plus I feed them everyday with the correct amount of calcium and D3. They eat sometimes but I know it is not enough (they always have a full plate of water to drink if they want). They always drink water. How come this is happening and what do to help them?