Peter,
I can completely relate to your fears, as well as your tendencies. I suspect they are fairly common as mostly human nature. There are a few things I have learned so far in my journey that might be helpful to you.
First, and I think possibly most importantly, make your absolute best effort to reframe your thinking about your TMS journey. See if you can change your mindset from one of it being a "program" to one of it actually being a "vacation". This is actually a very, very well deserved break from rules, "to do" lists, check lists, "must do's" and absolutely must avoids. Do something that is likely as uncharacteristic for you as it was (and often still is) for me - try to take your eyes off the prize.
Second, I assure you, with utmost confidence that when you "get to the end", EVERYTHING will have changed! That's actually exactly how I plan to know that I've arrived when I get there myself. Reality is only ever your perception at any given time and you're obviously well aware of self-defeating thoughts. They are powerful, formidable opponents, not to mention self-fulfilling prophecies. If you tell yourself (even without realizing that you've done so) that "I will be stuck with the reality of a compromised physical with no hope" then you've left little room for the possibility of an alternate reality.
Third (which I've just truly realized very very recently), if you are a perfectionist (which you likely are), remember that you have arrived here with all of your perfectionist traits running the show. Don't get me wrong, I can see the value in my perfectionist qualities in certain areas of my life and I am very grateful for them. TMS recovery, however, is one of the areas perfectionism has become a hindrance. Perfectionists (myself included) are notoriously unskilled when it comes to self-compassion. We are determined, we WORK really hard, we don't accept anything less than absolute, and we have expectations - boy do we have expectations - especially when it comes to ourselves. Give Pete a big hug. Cut him a break. He's been through a lot and he's still hanging in there - he deserves respect and admiration for his courage and strength, after all he wouldn't have gotten this far without it. There aren't any magic words or miracles that occur reaching day 37 on or before day 37. Give your diligent student/worker side a pink slip for the TMS work - he's not going to do you any favors here. You'll benefit the most from your TMS journey if you put the Pete who reads on vacation in the driver's seat for this one. Make it as pleasurable a journey as you can. There are no deadlines, there's no graduation, and you might find (as I have recently) that the more you relax and enjoy learning about the fascinating person that actually is you, you actually stop looking for the finish line, just like you don't look forward to the last day of vacation.
Forth, in the spirit of being kind to Pete, if pain meds help to lessen the pain then right now they are part of the solution. That doesn't mean they will be forever part of the solution. Try to stay in the present (as nearly impossible as that is for many of us). Do your best not to think about 10 minutes or hours or days or months from now, just try to keep your focus on "now". What does Pete need right this very instant to feel loved, valued, cared about, strong, and comforted? And, to the best of your ability, make your very best effort to give it to him. Try not to overwhelm him putting in vast amounts of information or digging up issues faster than you can process them (it's easy to do, I'm very guilty of it myself).
Happy Healing!
Incidentally, please disregard the "tms guru" that appears with my avatar. I don't profess myself to be anything of the sort, merely a curious learner who asks a lot of questions!