I was trying to think of something like this so I wouldn't be able to take my A-levels, and so would get my predicted grades. I couldn't think of any good illnesses though, and it's hard to catch them. i was going to eat loads of salt until I went into a coma (someone said you could do this) but it was a bit risky as I didn't know how much would be enough, and how much too much. At the end of the day I failed because I didn't have the guts to hospitalise myself, and I didn't get appendicitis.