I've been laughing my ass off through this whole thread!!!!
I have some friends that got giardia among other water borne illnesses when we studied abroad in Brazil. We were seriously worried about their lives. It was horrible for all of them, all 5 were in the hospital in the middle of the Amazon for several days. A scary ghetto hospital with dirt on the floor and smears of blood on the walls. One girl got so weak from the fever and diarrhea that she could barely walk for 2 weeks. It was horrible. For reference, they got diagnosed with Giardia, amoebas, and 2 parasites that I forgot the name of. If only the cooks had figured out when we asked to drink only bottled water that this meant we wanted them to wash our food in the bottled water as well.....
I highly recommend avoiding giardia. Really.
Fake the ear infection. It would totally be believable I think, and ear infections can be excruciating and keep you out of work for at least a week.