I dont really like the idea of real world diseases but i think @thegirlygamerx has a good idea. I would like it so sims can break and arm or a leg and be stuck with a wheelchair or crutches for a couple of days. I also like what @leo3487 mentioned about there being consequences about not going to the doctors. Colds can come and go of course. But have stuff like a flu shot or if a sim has the flu make it so they cant go to work and maybe have to go to the doctors to get some medications to go back to work and feel better? Have family doctors sims can go to instead of the hospital?