thats a whole bucketload of questions. 
i think for me, the hyperfocus bit is that i have just as much trouble turning my focus *off* again once its actually attached to something, as i do getting it hooked in the first place- also there is a bit of a thrill in feeling like you’re acheiving something when you spend so much time floundering- when i’m on a roll i don’t wanna stop cos i never know when the next one will come around. its kinda like a little kid riding a bike for the very first time without someone holding onto the back- i don’t wanna stop pedalling cos i know i might lose control and fall off, which’d hurt, and i’m not confident about if or when i might manage to repeat the amazing feat of keeping my balance and travelling at speed unaided again- you just cling onto that moment of hard earned awesomeness with dear life! 
with your shoulder- the unknown, or knowing that whats coming next is gonna be hard or daunting- thats like the best fuel ever for procrastination. the pain you know feels safer than the unknown might- its tangible, familiar, you know you can handle it- because you already are handling it, etc. this sort of thing has kept me from getting a job for years now- even though realistically i know i can and will handle it -if i put decent plans in place and stop picking on myself and setting unreal expectations- its just gonna be a bit of an uphill struggle for a while while i learn how to cope- which isn’t something i enjoy. i don’t enjoy not being employed either… but at least i know it- its familiar, and safe. as far as i know nobody is gonna fire me for not sitting infront of the tv organisedly enough, talking to the cat using innapropriate language, or showing up too late for a shower.
focusing on the negatives is a misguided coping strategy- subconciously you’re preparing yourself for the worst so you don’t get a horrible suprise, and warning yourself that nastiness is pending, to avoid an unexpected unpleasant experience- being aware of problems is a practical thing, but perspective is important and the balance easily gets way off. if you’re like me then you’re probably also overusing the whole ‘rabbit in the headlights’ respose that says ‘if i don’t do anything, stay very still, and shut my eyes…. maybe it’ll not see me and go away!’.
obviously thats not the case here, and you’re just postponing the inevitable, but it sure as hell feels nicer to go “lalalalalalaaa” with your fingers in your ears and your eyes closed, than actually sitting down, taking a deep breath, and wading through a whole pile of daunting, concentration-requiring stuff does…. for a while, at least.
there does come a point when your eyes start to hurt from being screwed up so long, and you can’t sing with your fingers in your ears quite loudly enough to drown out the knowledge that the poo is heading rapidly towards the fan, and you can smell it pretty strongly…. and then if you’re anything like me, you desperately start playing catch-up and cursing yourself for not getting on with it earlier. but then hyperfocus and adrenaline kicks in, you wing it, and somehow it all turns out ok… usually. but urgh- the stress… so much stress.
the right medication might well tune out the background noise in your brains little radio receiver enough that you can focus and get things done with much less drain on resources. i know that every time my dose of straterra has been increased i suddenly realise a day or two later that i feel dramatically much less foggy mentally than before, that i’ve got just a few thoughts at a time going instead of the previous usual swirling bucketload, and that i can complete a task…. say… like cooking a meal- that involves lots of co-ordinated moves and quick responses (adding things at the right time, getting tools from drawers, dodging whiny cats, remembering why i went to the cupboard, adjusting the heat, etc) without constantly second guessing myself, going blank, and walking in circles- just a little bit easier. my tension levels drop a bit, my impulse control gets better, and my sleep pattern balances out (i used to struggle insanely to get ready for and into bed, and then wake up late feeling groggy).
obviously you are still gonna have to work when you’re back at school, just like everyone does- new information and concepts probably are not gonna magically just jump off the page, crawl into your brain, file themelves, and then pop back out again upon request while you just sit there openmouthed picking your nose (i wish!). but if you can get the right support for your ADHD – maybe get funding to see a learning styles and needs assessor type person, someone who knows all the strategies and who can get you a dictaphone or whatever works for you (personally i think i’d need a study coach to check in with every day for 10 minutes or so- to say “ok, whats on the books for this week? lets make a planning sheet?! did you do that essay last night? where did you get stuck? how can we fix that? and generally prompt me, make sure i stay on track, and encourage me to resolve problems instead of procrastinating) there is no reason why you shouldn’t be able to succeed.
like anything, i bet it’ll be much easier and smoother sailing if you don’t try and mentally or practically bite off more than you can chew- cos thats a recipe for *feeling* like a failure, and tends to lead to my deciding to just give up on a whim. you might need to do one course at a time, focus on one hour at a time, follow a different schedual to the majority of the students, have tests delivered in a different format, or whatever- but there is pretty much ALWAYS a way of making something work, its just a case of finding it, and being stubborn enough to follow through.
going back to your operation- what i’ve started doing is scrapping confronting the big long term plan (cos when i see it or try and think about it, it looks huge and unsurmountable, i start to feel very sick, my mind races in circles, i find myself desperately flapping my arms, and get the urge to get under the duvet and hide)… and getting onto a *little* plan.
i can’t ‘go out and get a job’ today, cos quite frankly, the idea makes me want to pee myself, but i can cope with maybe… reading an application form. just looking at it. nothing more. and tomorrow i will tell myself that can scan and print a copy of it, and doodle some ideas down in the boxes- thats all. and the next day i can organise them- get it all tidy- thats all. then the next day i can type it up on screen, and shut my eyes and press ‘send’. at some point, i will end up in a job. but it’ll not be tomorrow, and i won’t be desperately treading water and wondering what the hell happened, to quite the same extent as i might otherwise be.
maybe you could do the same thing with your surgery? baby steps. tell yourself that its gonna happen- but later, and take little steps towards working out and setting up your college moves -one every day, until the plan comes together and you’re doing it without even realising it, and it turns out to not actually be half as bad as you’d imagined- maybe even awesome. you could end up wishing you’d done it years ago- that sort of thing happens. .