Considering the pretty obvious excitement, written in the Torah itself, that B'nai Yisra'el had about receiving the Torah, it seems contradictory that they would be sleeping on the day the Torah was given. We read about all the warnings not to touch the mountain, and the declaration of "Everything G-d tells us we will do." There is even another midrash that says that the Jews requested the message directly from G-d even though it was suggested that Moshe deliver the words to them, at first. It was only after they heard the voice that they were scared and requested Moshe to be the one to convey it to them.
So, from all this, how does the Midrash infer that they were sleeping and had to be awakened for the giving of the Torah?