Lori, maybe I don't know you well enough for it to be appropriate to send you a cyberhug but if you want it, there's one in the air for you from me! I was just looking back at some of your past posts - no wonder you're feeling at the end of your tether. You are not horrible - you're dealing with a harder lot of stuff than many people ever have to.
Concretely, the most obvious practical thing from your post is that you need a better solution than that safety pin! Is your DS due a new brace that will solve that problem, or can other people who've experienced them or his carers help you to find a solution that will let him go to the toilet unaided? That seems like a pretty basic piece of functionality to expect, for his dignity as well as to take a burden off you. He's 12, right? Maybe he could take responsibility for leading the problem solving on this one.
About when to find time for meditation - I've BTDT in the sense of having times when life was so overwhelming that there seemed to be no time at all for me. I think there are no ideal solutions, but "put your own mask on first" definitely applies. You need to look after your own needs, or you simply won't be able to keep looking after others. Also, you know how people tell new mothers "sleep when the baby sleeps"? That never worked literally for me, but the principle is good: any time you know you are not just about to be interrupted for something urgent, make that your meditation/nap/you time - don't squander it on housework or other stuff that is, ultimately, less important and more interruptible.
I think generally, it's important to distinguish between stuff that really is important to keep on top of on a daily basis and stuff that's not. I think in your place I might, for example, decide to keep chasing my DS about his exercises, but tell him that I simply wasn't going to chase him about his maths until, say, 2011. If he knows you're not going to be responsible for whether he does his maths, for a while, he may (after a bit) pick up that responsibility himself - particularly since you say he's interested in science, which he'll realise at some point requires maths! - and if he doesn't, he won't come to long-term harm by doing no maths for 4 months; he'd just have to do more in 2011 (tell him that, too!)
