dr_pie
1) while not necessarily common, your details going to the medical department is just to check your potential eligibility to get a Class 1 medical, which is necessary to be an ATCO. You will know what you put on the form which may have caused this, it may be worth taking a look at the Class 1 Medical requirements on the CAA website for more info and/or a better idea of what they are checking.
2) The usual shift pattern (with slight variance) is a 10 day cycle, 6 days on and 4 off. Start with 2 mornings (0700-1430), then 2 afternoons (1430-2200) then 2 nights (2200-0700). Less people needed on nights, so if not rostered on nights, you do two additional mornings or afternoons instead of the nights. Followed by the 4 days off. And so it continues...