Worked rotating shift work for many years. Worked XYZ shift which wasn't quite as bad. Swings, days and graveyard one week at a time with weekends off. Then there was the dreaded ABCD shift that was 7 swings two days off, 6 days on and 1 off and 7 graves straight with a 4 day long change then start over again. It was hard enough to work that schedule but some brilliant SOB decided we should change the rotation from swing, days, graves to days swings, graves. Screwed me up royal and has effected me to this day with sleep problems though I worked that schedule back in the 80's.