What surgery did you have? Did you have a mini-laminectomy or full laminectomy with vertibral fusion or did you get the artificial disc?
Just because you have followed dr's orders doesn't mean that you cannot or will not have either a relapse or even more difficult to deal with, another disc with herniation/tears/bulges. Disc faliure is not uncommon and if you had fusion, you probably had another disc that was going bad but had not caused you problems yet and with the repair/stiffining of you l4/5 space another disc above or below may have been put in the perfect condition to fail.
If you got relief from the first surgery, you will probably get great results form a second if it becomes necessary.
This is just an idea and I am not a doctor at all.
i hope this helps