The most common ejection injury is a compression fracture of vertebrae but with rocket assisted seats these are rare. More likely injuries occur when meeting terra firma again. Obviously, high speed ejections are another matter. In my case, with a rocket seat, I did have a compression fracture but I was in my mid 40s at the time and I broke an ankle on landing. No after effects to date. As to thinking time, it rather depends on whether it is premeditated or not. Again in my case I was back on terra firma 49secs after starting my take off roll and am very glad that I did not have (or need!) time to think about it.