I’ll take 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.
This is nothing compared to some of the shit in this thread, but I accidentally accepted shifts at three jobs that had me working 24 hours straight. Started loading in for some sort of concert at 4am, then at 9am I went for a shift at a cafe, at 2pm i left for a shift at a grocery store, at 10pm I left to start tearing down the stage I set up in the morning. I was finally done at 4am, 24 hours later. Got home at 5am and as I was washing up all my joints cracked and I had the longest fart ever.
*Accidentally because the stagehand job was on-call and they only called me like once every few months. It was good money, so I accepted it on the spot. WOOPS.