I’ll intellectually/emotionally/physically hard as answers. For me its either 12 hours straight “punching tubes” on a very large scotch marine firetube boiler at the beginning of my career or Easter around a decade ago when I was working with troubled teens and had to engage in 5 separate protective holds in one 16 hour double shift. The former was all physical and the latter was a combination of emotional and physical.
Was doing pager duty support and there was a bug in a pipeline which was preventing a vital report from being generated. It had to exist by 8AM UTC and finally got it working at 5:30AM. My company would have lost its license to operate in a certain state if the report had not been generated.