Hey mate, if you feel really shit, don't push yourself, just take a rest. Go with passive study if you need to, like, reading over notes or mistakes you've made in previous exams, instead of actively doing new questions.
Because if you're really sick, you're going to feel real lethargic when you study, making it damn inefficient - you're not going to burn new information into your mind. You can use that time instead to rest and recover, until you feel energetic enough to study again.
To be honest I don't find setting a quota of exams to do very helpful - just do as many as you can in that time frame, you don't want to stress and rush over exams without going back through them thoroughly, so you can meet your quota. Going over less than 15 exams extremely thoroughly can really push your score up very rapidly, more quickly than by doing 20 practise exams over the week.
I think you're putting too much stress on yourself, take some time to rest, because that's what your body needs at the moment.