Not all of us are grouchy.
I think day shift is stressful where ever you work at. I work in a hospital and you've got to do your patient care (baths, treatments, meals, meds, etc.), explain things to them, & deal with extended family. Then there are the tests that have been ordered. And, at least two phone calls to go with each test. I work in critical care and there has to be a nurse accompanying the patient where ever he/she goes, not good when you've got no better staffing than on night shift. And, then there are those lovely professional doctors to contend with. And, then here comes more family to ask the same questions all over again, instead of finding the family member who has been here all day to get the answer.
Now, mind you I realize that night shift is busy too, but generally there is a lull in there about 1-4 am. Families have gone home, or are catching a nap. Not many tests are ordered for the middle of the night, and thank God, most patients sleep a LITTLE during the night (docs too).
And, then there are those emergencies that catch both shifts equally and throw the best-laid plans right out the window.
Ok, I'm only occasionally grouchy, but I try to smile a lot.