I had a terrible problem with my back a couple of months ago. I have no idea what happened, but it was completely thrown out for some reason. The last time I went to the doctor for it, he said he could prescribe some pain medication for me, but it was likely caused by my body not being used to lifting children on a regular basis. This time, it required narcotics just to be able to get out of bed and stand up without crying out in agony.
Praise God that I am not generally dealing with serious health issues such as these, but a thorn in the flesh can really help you focus on God. In fact, as difficult as it was for me to do so, I was able to thank God for the pain, as it helped me focus on His strength to deal with the issue and kept me from sinning. That was a huge growth opportunity that God provided for me, and it is all due to Him that I was able to do such a thing. It is very tempting in such a time to doubt God and wonder why you are being punished. It is only through Him and His glory that we are able to turn our problems and our thorns into something useful and beautiful.