If your stress levels exceed 50, I believe, you'll get sick. Note that this only works once, and if you exceed 50 stress points after this cut scene, MC will go on an insane shopping spree and leave you with only half your money. Also, it's important to to note that you can only call the guys whose number you already have on your phone. For example, even if you're in Shuu's route, if you don't have his phone number, you won't be able to call him to nurse you back to health. ^^