Why did Ya'akov find it necessary to exert himself and sit up on the bed when Yosef arrived?
Rashi and Seforno: Because effectively, Yosef was king, and one is obligated to honor a king. 1
Rashbam: He actually sat on the bed with his feet on the ground. 2
Moshav Zekenim: He wanted to show that he was healthy, lest people say that his mind was befuddled, so his gift was invalid. 3
Rashi: When Moshe honored Par'oh (See Bo, Sh'mos 11:8) and Eliyahu, Ach'av (see Melachim 1, 18:46) they took their cue from Ya'akov.
The Rashbam says this (not to answer the question, but) in order to explain Pasuk 12.
Da'as Zekenim and Hadar Zekenim say "lest people would say that it was Matnas Shechiv Mera" (which is valid, but the giver can retract) and his mind was settled.