Given the symptoms you report (it's hard to sleep, you emotionally react all the time, tiredness…) and given the problems that worry you (injury, financial…), you could be experiencing some type of depressive disorder. A back injury and its consequences can provoke depression but it seems more likely that your personality is the real cause for your depressive state. You'll have to be strong to overcome this condition.

Ridding horses may at first appear more interesting than swimming but I believe that swimming could be very useful for your medical recovery. Perhaps in time you can completely recover from the injury and become able to ride again. In the mean time you'll have to struggle with the life lessons in front of you now. Believe me, there are much worse injuries and illness compared to your back injury. Any support from your relatives and friends would be valuable.