. . . at my job we're on our feet our whole shift (12 hours, yay), and even if it's slow (which is rare) we're supposed to find something and clean it.. I don't know if that's just our company 'culture', but it's exhausting.
That's similar to the "company culture" at my equine job. I guess we're somewhere between an emergency clinic and a regular small animal clinic, since we do preventive care but also do 24/7 emergencies and intensive medical management of colics, dummy foals, etc. During the day, if there are no inpatients or outpatient appointments at the clinic, you are expected to do things like dust and de-cobweb the clinic, clean the refrigerators, rake, anything but sit around. If there's very little to do, someone goes home early.
The only time we can stop running our feet off is at night, when we are allowed to take naps. If you have a colic that's on autopilot (comfortable, fluids running OK), you do stuff like run the autoclave, vacuum the office, etc., until midnight or so, then put your cot outside the stall and catnap. I've had a couple nights where I slept in the afternoon before coming in, worked the first half of the night, took naps between treatments, and went out on the road with one of the vets the next day. There are also nights where you are running around like a fool trying to take care of several foals.
For the record, our overnight shifts are long -- start at 3 or 5 PM, depending on how slammed the day people are, and work until 7 AM the next morning.