Rashi on Genesis 47:31/רש"י על בראשית מ״ז:ל״א

1וישתחו ישראל AND ISRAEL PROSTRATED HIMSELF — The proverb says: Though the lion is king “when the fox has his time, bow to him” (Megillah 16b).

2על ראש המטה UPON THE BED’S HEAD — He turned towards the Divine Presence (the Shechinah) (Midrash Tanchuma, Vayechi 3). They (the Rabbis) inferred from this that the Shechinah is above the pillow of a sick person (Shabbat 12b). Another interpretation of על ראש המטה He bowed himself in thanks FOR HIM WHO WAS THE CHIEF (ראש) OF HIS CHILDREN — in thanks because his children were heart-whole with God, and none of them was wicked, for even Joseph who was a king and moreover had been a captive amongst heathen peoples yet maintained his righteousness (Sifré ואתחנן 31).