When I tell people I'm in pain (or similar), I'm usually trying to convey "Hey, sorry I am not at my best. I'm not trying to be rude. I'm not trying to bark at you. If I'm failing to get all the info, it's not for lack of trying or being too lazy or disrespectful to pay attention. I'm just doing the best I can right now and the best I can isn't that great."

And that's usually not how it gets interpreted so I do a lot less of that than I used to do.