I used to get terrible stomach aches after brushing and it was enough that I completely stopped brushing for a long stupid time. Even when I made myself do it I ended up with this tons of skin falling off inside my mouth every morning if I brushed before bed. It was absolutely nasty. When the dentist used those plastic trays with the fluoride foam it would leave me curled up on the couch for the rest of the day in pain.
One day my wife suggested that maybe I have a problem with SLS and I switched to sensodyne pronamel which was the cheapest SLS free toothpaste I we could find and all of these problems went away. I'm now a regular brusher and feel stupid for not figuring it out years ago because my teeth have suffered from my ignorance.
In the interest of being thorough I switched back to my old toothpaste for a day and the symptoms immediately returned after just one night-time brushing. Sure I could go through many more changes to try to pin down exactly whether it is SLS or something else that's different between the two toothpastes I was using, and I recognize that, but SLS was enough of a reason for me to switch and I'm happy now.
Sensodyne is a brand, not a specific toothpaste, and some of their products do have SLS, but sensodyne pronamel, at least here in Canada, does not have SLS.