I agree with 5jj, you can pretend or you can enter the class feeling down and pretend you have got that problem or one one of your family members had it and he/she didn't let you sleep well the night before, because she kept coughing all the time. You can also pretend the day before you went to a doctor and let them ask you why and through doing pantomime, elicit the words (let's be hopeful they know the words, if not you can let them know). Pictures are also a good way as 5jj mentioned. I also cut up different pictures of illnesses and the proper words for them and let groups of 3-4 match them. In this way they can learn some new health problem and after getting feedback I work on their pronunciation. I use a picture dictionary to make the cards.
Being a non-native teacher, I'm so thrilled being in such a superb forum.
these pictures, many of them copyright free.