I saw this article in the LA Times the other day and I haven't seen it posted here. The Readers Digest version is that it tracks all sorts of theme park injuries. While they are very rare overall, oddly enough, Space Mountain leads the pack. I'm surprised that it is higher up on the list than some of the more extreme coasters at Knotts.
With 120 injury reports from 2007 to 2012 (and those include things like motion sickness, slipping and falling while boarding, etc.) it's clearly still very rare even on Space Mountain - but it's food for thought for me, personally. I stopped riding Tower of Terror because it was giving me headaches. The injury reports themselves are quite interesting. It seems that 98% are "user error" (there's one where someone had a seizure...but then said that they had a history of seizures and hadn't taken their meds that day) but there are a lot of other people who have headaches from the coasters. There's also one guy who had a subdural hematoma after riding Maliboomer, Big Thunder Mountain (9 times) and California Screamin'.
Nausea, dizziness, fainting are most common theme park ailments - latimes.com