The things that break ablution: A person praying falls asleep on the prayer mat for about an hour, and the effect it has on his ablution

A person prays the night prayer, then he is overcome by sleep so he lies down on the prayer mat and sleeps for about an hour. After he wakes up, should he carry on praying or go and make ablution again?

If he was asleep for this period of time, it must have been a deep sleep, in which case he must go and make ablution again.