Bryant, for some people yes, a lighter weight can allow poor form whereas the right weight will enforce good form. When I hear of someone getting injured at the end of session with a light weight, this is one of the thoughts that come to mind. It's easier to know when you're cooked with a moderately heavy weight than it is with a light one, which is why I counsel dialing back the reps, dialing back the sets, and using a proper weight.
I have a personal anecdote on this subject. I was at the first Easy Strength workshop, and we were doing stations with increasingly heavy weights. One of the lifts was the barbell deadlift. Pavel came over to me, very nicely took me aside, and told me that my deadlift form looked pretty terrible. I told him that I never deadlift light weights and didn't really know what to do with them. As soon as we had 225 lbs. (100 kg) on the bar, my form was fine.
I know nothing of the original poster's background but it's been my experience that most adult men shouldn't be doing much in the way of swings with a 16 kg unless they are completely new or recovering from injury. I imagine that, were I starting out S&S today as my introduction to kettlebells, I'd switch to a heavier weight before I ever completed 100 swings. When I got my first kettlebell, I felt like I was thrown all over the room when swinging a 16 kg - but 10 days later, I ordered a 24 kg and never looked back.
The best scenario here, since we're giving Internet advice, would be that the original poster, _after_ he gets cleared by his doctor, posts all the relevant details of his background including his age, height, and weight, and also includes a video of him swinging a kettlebell. Then and only then might we be able to offer practical, specific, and not just general advice.
-S-