Welcome, and oof, that sounds nasty to deal with. I'm severely disabled myself, so I know what it's like when something like this completely changes your life, although in my case it was a lot more gradual and I'm not dealing with that level of pain. I do have fairly profound cognitive symptoms. Even if they don't improve, you get more used to dealing with them. Look into various types of reminders, software and smartphones and the like. One of the reasons why I have to track what I eat is because otherwise my partner comes home from work in the evening, asks if I've eaten that day, and I don't have the faintest idea.
I'd go to a medical professional for the exercising. A physio, perhaps, but I'd start by asking the centre who treated you for the trauma and its aftereffects. That said, I'd maybe consider a mini exercise bike, also sold as a pedal exerciser (I've got this one
http://www.amazon.com/Drive-Medical-Folding-Exercise-Electronic/dp/B002VWJYSE/ref=sr_1_2?ie=UTF8&qid=1315510690&sr=8-2 after my partner accidentally killed my previous, heavier model while hoovering). You use your own seat, so you can sit back in an armchair as if you were on a recumbent exercise bike and be fully supported from three sides. If you're not moving your upper body, I'd guess that it's less likely to aggravate things. Alternatively, perhaps sit on an ordinary chair, put the exerciser under a table, and hold onto the table to keep your upper body supported. But really, please check this with a medical professional, I'm just guessing here. I have a nice tame physio who was originally assigned to me when I had acute calcific tendinitis four years ago, and as she's great with the ME/CFIDS too, I get hold of her every now and again to ask more questions.
One thing that may cheer you up is to know that it's possible to lose weight without exercising if need be (I am), and that it's also possible to get a beautiful toned body without a vast range of exercises. Joyful Loser looks fabulous from running alone, for example.