Musar for Shabbat 138:13

The latter two questions may be adequately answered by the halachic ruling in Shabbat 69 that a person who is lost in the desert and has lost track of time should observe six days of work and rest on the seventh day, starting his count from the moment he does not remember which day of the week it is. The reasons for this ruling are explained by Kley Chemdah on פרשת כי תשא.