Something I have noticed, in addition to people saying "You look ill.", is that they'll sometimes say "You look tired." when you haven't slept in a bed. I try to always sleep in a bed to get that rested bonus!
I am a dark elf and every time I hear them comment, I have Rockjoint. You get Rockjoint from fighting animals mainly, like bears and other bigger animals. I have gotten it twice in 18 hours of play.
This reminds me of the very first time I came out of the sewers at the start of Oblivion and within a couple minutes I had contacted 2 diseases.
I just fought two skeevers and then walked into an Inn where a guy said 'you don't look too good' and I checked and I had witbane. I have never heard anybody say this unless I did have a disease.