I have twice seen posts on this board about people amputating parts of fingers. I have to admit that when I see "rotary cutter" in the subject line I hesitate to click, but then I think that whatever it is, it's probably best to read it and let myself be reminding once again of the dangers. Mine jumped over the edge of the ruler one time and nicked me, and I no longer use it with any part of myself or anyone else on the business end of it.
Somewhere on Youtube is a video showing two women taking turns cutting from alternate sides of a table toward each other. It is speeded up, which makes it look all the more risky. They may be more coordinated than I am, but it gives me palpitations, and I can't watch it.
One tip that has helped me a lot is to coat the underside of all my rulers with rubber cement. It takes a long time to dry (at least in our humid climate) but it is the best thing I've tried for keeping that ruler where it belongs without any temptation to hold it dangerously far ahead. Also, I have abandoned the old cutter that has to be clicked shut in favor of one that closes automatically when the handle is released. This is well worth getting. I have heard of too many people who have dropped them, putting their feet or someone else's or a pet in danger.
Thanks for posting this, and I'm sorry you hurt yourself, but relieved it wasn't worse.