Interesting question. I responded disorder because it's in the title and I was corrected in a thread early on by referring to it as an illness.

I guess I can now see how it isn't an illness for sure because you can't take an antibiotic and make it go away.

Injury - Nah, the closest may be a traumatic brain injury but an injury to me focuses on the physical body.

Now, the difference between disorder and syndrome? They kind of mean the same thing to me. Unless a syndrome is cyclical. You got me.