Alfers,
Hey. 
I'll start with Ankylosing Spondylitis is a real pain in the back! {all puns intended} AS usually efects men, but some females do develop it.
So I was not feeling "right" from age 13 to 18. Joint pain, weird fevers, some rashes that would come & go, passing out, seizures, knee pain, spine/back pain, and real bad jaw pain.
All of this was dismissed for all of that time as "growing pains" "depression" "it's NORMAL" (I like that one the best). And still being able to work, go to school, work out & do everything I basically never questioned them. So these symptoms got WORSE. Bloodwork @ 16 started showing + for RA and weird immunoglobulins. MD said it was genetic & I'll get lupus or RA or something when I get old (yeah ok).
Long story short. Emergency surgery in August 2001 had me with adhesions, a benign tumor grapefruit size on the ovary-adhered to the appendix and also formed a connection to the lowel bowel. Wonderful eh? Plus a belly full of blood for good measure. My PCP who's a saint...ran EVERY TEST IN THE BOOK. Only Lymes showed up and all the findings for RA.
Treated for Lymes (then it turned to NeuroLymes) that the CDC dated as at least 10 years old [& had also mutated and become antibiotic resistant]through DNA analyses; with antibiotic cocktails (GRAMS per day...30 to 40 pills! barf) from 2001 till January 2004.
This bacteria gone undiagnosed & untreated left a motley crew of AI issue. RA, Crohns and AS. The Lymes was a picnic compared to the RA and AS and Crohns. I mean, Lymes is bad...but having a chronic progressive disease that dose a number on ya every day is...well...the pitts.
AS is part of the inflammatory processes. Likes to hang with RA and the like. So it's basically like a joint fusion; or if you wanna get Greek: Fixed, stiffened, proktos!, 
ankylos!, held together by adhesion. It's caused by diseases like RA or other AI diseases, trauma, could be congenital (like Hank Williams!) or from surgery.
My complaint with it is the back spasms. It's a wrap around pain that takes your breath away. Diazepam breaks the spaz most times. Enbrel helped the most. Just trying to keep upright is terribly difficult.
So there I am in a nutshell. I hope I gave Ankylosing Spondylitis a little character & made it relateable. I wish you well.
erin