Spleen injury is one thing to watch out for, as I discovered when I broke my ribs in a 12mph OTB. A broken one is like a leaky bag of blood that can drain your system and then you’re a gonner. Symptoms were nausea, fainting and blood in urine, which came on a few hours later.
For some reason we have this organ tucked just under the bottom rib on the left side, just waiting to be pulped if you fall at the wrong angle.
Unlikely this is the case for the OP, but worth bearing in mind when forumites start saying it’s “just” a cracked rib.