oh coniston, i'm so sorry. i have a daughter that age ....but i can only imagine the shock and distress to her poor family and friends.
could you think about doing doing something other than class teaching? if things have really got to the point of no return? (in terms of your energy/ resiliance-sp?)
i am considering applying for learning mentor jobs. that way you get the rewards of helping needy children but without the stress of all that planning/ assessment etc.
for me, this would mean a pay cut of about 30% which fortunately we could manage.
if you feel this strongly, then i think you need to think about taking a bit of a career diversion to lessen the stress.
i am finishing a diploma in SpLd this term- one reason why i left was to finish my studies and do a bit of voluntary work to help my transition into SEN roles.
as you can see (compared to yesterday's post!) am feeling a bit more positive today myself, and i am a bit confused about but also wanted to give you a bit more detail about how i've planned my escape route from class teaching.
you have to put yourself first, at the end of the day. if its that bad, could you possibly afford to do something else a little less well paid, and leave at xmas?
by the way, i was also part time, but studied/ planned on days off and still managed to find working 0.6 utterly overwhelming (as i had to change key stage in my last year as well as study!)
remember what i said... put yourself first. 
good luck to you x