וַיֹּאמֶר לְיוֹסֵף הִנֵּה אָבִיךָ חֹלֶה "And he said to Joseph, behold your father is ill" (Bereshith 48:1). It says in the Sefer Hasidim, that one must make an effort not to say anything that is not good, to one's friend. In view of this, how do we understand the fact that they said to Joseph that his father was ill?
The answer is that the Gemara tells us that till Ya'aqob Abinu, 'a"h, (Jacob), no one became sick before dying. Everyone was in full health when they passed away. Jacob requested, as Rashi puts it, that a person would first become ill before passing away. That way he could give instructions to his household and also, it prepares the others for what is about to occur.
In fact, before this, a person used to sneeze and die. This is the source for the custom of blessing someone for life and health, when he sneezes. Ashkenazim say (in Yiddish), Gezundheit, which has been translated in modern Hebrew to Labriuth, which means "in [good] health". The custom that we follow in our home is to say Hayyim Tobim, which is a wish for "a good life".
(See Dibrei Mordekhai, Wayhi, Parparaoth)
parasha, Vaychi, Vayechi, Vayehi, Wayhi, sneeze before dying