Okay.. I would take the prescription to your doctor and explain that you didn't fill it at the time because you have found in the past because you don't like the way it makes you feel (panicky or a bit spaced out..). You've heard that this is because of the way endone is instantly released once taken, and that you might be better off taking a sustained release form of the same medication to avoid the side effects.
By showing the doctor the script - which is clearly in your name, and which you chose not to use - it should provide peace of mind that you are unlikely to abuse a prescription for something similar. You have suffered pain, rather than take a pill you are worried about taking. Ask him if he could possibly write you a script for the sustained release version of oxycodone, but would prefer it to be low dose because you understand you wouldn't be able to break the pills in half if they were too strong for you.
By expressing concern and respect for the drug, and showing that you are cautious about what you are taking, you should have no problem finding a doctor to write you a replacement prescription for something more suitable for you. Maybe add that you wish you'd come sooner because you've been enduring terrible pain, and hadn't realised there was an alternative to the instant release oxycondone (endone). In effect, what you would then be given is oxycontin. But BE CAREFULL. It's a slippery slope, but you fall upwards.. to higher and higher doses as tolerance increases. Then one day you figure out that your pills work just as well for your emotional pain as they do for physical, so the day your cat is run over you decide to medicate.. and before you know it you have a fullscale addiction on your hands.
PLEASE be careful. I started out 5mg endone 'once in a while' and ended up on 80 mg oxycontin, taken five times daily - at my worst! Somebody on a forum just like this, warned me that it could happen to me.. and I wouldn't even know it was happening. Told me to stop before it was too late. Now here I am writing the same kind of email to you. I didn't listen. But you still can. PLEASE don't let oxycodone get it's hooks into you. I would recommend the oxycontin simply because it is sustained release, and if taken correctly won't give you that intense 'rush' that mimics heroin. You'll have moments of feeling quite 'all is well with my world'.. and a general feeling of wellbeing, as well as releif from your pain.. so long as you take it correctly. Start crushing, snorting, shooting etc and you're history.
Be careful. Please.