What is Work up?
Work up is (verb) 1. to develop I find it difficult to work up any enthusiasm for my job. 2. to do some hard work to make something happen I’m doing some digging to work up an appetite. 3. to work yourself up into a state to make yourself annoyed and worried by something He’s worked himself up into such a state about his exams. worked up
source: Easier English, Student Dictionary Upper Intermediate Level