Ah, "Post-Nasal Dick": the second in a long string of fantastic comedies.
In this episode, the Solomons learn what it is like to be ill-- and, of course, having never experienced the sensation before, they think they're dying, causing them to both wax sentimental on all their missions together, and possibly even blow their cover!
Filled with wonderfully snappy dialogue ("You know, you sound just like my mother." "That must be very confusing for you.") and outrageous situations, "PND" is one of the best episodes in one of the best shows of all time.