Actually they let me take a pass when I was called in. It was when I'd started having heart palpitations and didn't know wtf was up with them, and the anxiety surrounding the not-knowing-if-I'd-end-up-serving set of a bad attack of 'em...so I dunno, I think with certain complicated situations they'll be understanding about it.
'Course it may have helped that I looked like a deer in the headlights...at mine, they allowed a written explanation, even. So I scribbled it all on the envelope that had the doctor's note in it. Apologising for penmanship and spelling.
You've had so much trouble with the temp stuff, and taking into account green_trilobite's anxiety...maybe they'd accept that as reason to decline?