I think generally things that hurts you fall into two category:
- Things that make you sick but let you learn a lot from it, and from that lesson, you will not get sick (or as sick) when it comes to you anymore
- Things that make you sick and the part that hurt will not function as good as it used to.
Those are nice things that hurt you. Nice, as in it makes you stronger. It hurts but you're stronger after that. You learn things that make you able to fight it. I mean, there's a chance that you die, but when you didn't, you're stronger (oh dear there goes the 'what doesn't kill you makes you stronger' quote). It does not matter if you're exposed to more of the source, you can fight it now.
But some things hurt you and you become damaged.
Like when you got burnt or when your ankle is sprained. Or when the ligament in your knee is torn. You healed, and it generally won't hurt. But sometimes it will--when you touched them too hard, when you had a bad posture, when you give too much pressure, when the weather is bad--even though it's supposed to be healed.
You are healed, but you're not the same, and you will never be the same. You will not be able to do things like you're used to, because you're more vulnerable than before and the more you expose yourself to it the more broken you will be.
It's not nice, and it hurts, but you learn something from it too: it's not good for you. You have to avoid things that hurt you like that. Avoid the risks. You shouldn't play with fire anymore, you shouldn't skip your steps in the stairs anymore, you shouldn't play sports competitively anymore. You don't expose yourself to more of it--it won't make you better. If you do, you will hurt and damage it even more.
But sometimes people cannot differ these things well. Sometimes you are hurt and you don't know what kind of lesson you should take: does this mean you can handle it better from now on? Or does this mean you have to avoid this thing that hurt you forever?
Though I guess it's a thing that you'll figure out sooner or later anyway. I mean, as long as you want to survive, you will definitely learn about what kills and what doesn't kill you.
Else, just find a doctor.