Afternoon sleep, is it a vision or a dream?

Night and day are two ends of a vision, and it is not exclusive to one of them. Visions vary in truthfulness and interpretation, just as a daytime vision is like a nighttime vision. They may also differ in degrees of truthfulness. A vision seen in the early part of the night is slow to be interpreted, while one from the second half is quicker, varying with the parts of the night. The quickest to be interpreted are visions seen at dawn, especially at the break of dawn, and visions during the siesta (Qaylulah). The Prophet, peace and blessings be upon him, said: "The most truthful visions are those seen at dawn."