Does sleeping through a prayer during Hajj—with uncertainty (as to whether it was missed)—entail expiation or invalidate Hajj? Are there signs of an accepted Hajj, and what does it mean to not feel a change in one’s personality after Hajj?

The expiation for a prayer that one slept through or forgot is to pray it when one remembers it, based on the Prophet's (peace and blessings be upon him) saying: "Whoever forgets a prayer or sleeps through it, its expiation is to pray it when he remembers it." The sign of acceptance of an act of obedience is a good deed that follows it. Thus, your feeling of inner peace, high spirits, and increased obedience after an act of worship is a sign of acceptance. If it is otherwise, then repent, strive to turn to Allah, and continue to struggle against your lower self.