Hadith.1042 - Ali ibn Mahziyar asked about this issue, and Imam عليه السلام replied:
"He does not have to make up the fasting (sawm) or the prayers (salat), and everything that overwhelms a person due to God's will, God is more deserving of granting the excuse."
As for the narrations that mention the unconscious person making up all the missed prayers, or that they must make up the prayers for a month, or for three days, these are correct but are understood to be recommended (mustahabb) and not obligatory (wajib). The principle is that there is no obligation to make up the missed prayers or fasts.
