In deep sleep, there is no awareness of body, mind, and even ego. Therefore in deep sleep, the self becomes free from all identification and hence free from all complexes., all inhibiting factors that deprive him of the experience of his own self. He experiences his own self, that is ananda!
What wakes me up? Deep sleep is such pleasurable experience that nobody would want to wake up. Nobody wants to give up the experience of the deep sleep state because in fact it is the experience of happiness. But I am forced to get up. It is my past karma, it is my unfulfilled desire or ambitions or duties or preoccupations that force me to wake up.
Pujya Swami Viditatmanandji, Kaivalyopanisad