Funnily enough, I miss the weight of the 1D cameras. I ditched them as the 1DX (and X2) obviously moved more toward speed, and I had been using the 1Ds line for the sake of resolution/image quality. (Remember, when the 1Ds2 came out it was the only SLR which could match medium format for resolution at the time.) As the 5D line took up the resolution/image quality race, I started using those with grips. Still didn't feel right so I went back to the 1Ds3 and took to just stacking files to get higher resolutions and cleaner images. Now since the 5DS R I've not been able to justify sticking with the 1Ds3, and I got a Phase as well for when image stacking isn't an option and I need high quality in a single shot... but I miss that 1D feel. I miss the dimensions. I miss the grip. I miss not having a mode dial. I miss slamming those big batteries in. I miss the shutter sounds (especially the 1Ds2, which sounds like something from a sci-fi film). I miss the cushion shutter. Most of all, I miss the weight. Yeah, the Phase is just as heavy, but it's heavy in a different way, the balance is all off, and the very nature of it means it lives on a tripod, not in my hand. It's not the same as having a 1D in your hand all day.
... And I can barely walk, most mornings. Too much carrying heavy camera equipment and heavy music equipment. No one incident, just built up over a period of about three years. Two spine surgeries, some permanent loss of feeling in both legs, often have to rely on a walking stick in the mornings. I'm 30 and my back is more broken down than my father's, who's in his 60s.
I can still hold a 600mm shot steady at 1/100th without IS, but boy, I can't carry that lens to and from its destination. I can lift a 1D but I can't use it for a shoot. About 2 minutes of shooting is my maximum with gear like that now, handheld. Obviously a tripod negates that but there's not much advantage to a 1D when it's on a tripod; those things are meant to be in the thick of action.
Moral is, even if you don't have one big incident where your body suffers, carrying around heavy gear will build up if you're not a professional weight lifter. For OP it was one afternoon. A friend of mine developed severe muscle and joint problems in their left arm and shoulder six months after they happened to purchase a particularly heavy guitar, and was playing it nearly every day. For me it was three years. For someone else it might be ten years. But it'll be there, however sudden or slow it may be.
I love those heavy 1D bodies. My dream camera is still basically a 5DS R but in a 1D body. But yeah, it's not worth it. Never ignore your body telling you to stop. Doesn't matter if it's a heavy body or a heavy lens, a heavy bag full of gear, or whatever. Cut out what you don't need, and look for lighter alternatives for the things you do need. No piece of equipment, no matter how objectively great it may be or how much you like it, is worth damaging your body for.
