my son had it at 4 weeks, and had HiB at the same time - he was very very ill, blue lighted up to London, PICU, ventilator - the whole nine yards.
It was a terrifying time for us. He was in on Christmas day, and I spent Christmas eve at home with my then 6 and 3 year old. Did the whole Christmas Morning thing, and then went back up to LOndon at 10am.
That said, Christmas Day is the best day of the year for me, because on Christmas late afternoon, they took him off the ventilator - I had never felt such joy, and that cuddle, without all the pipes and vents - just the best cuddle ever. I cried and snotted all over him, while laughing.
We were told, like others here, that it takes 5-6 days to get through, and that 1 in 1000 will require some help and 10 of those will require the support that DS needed. When they start to recover, they "bounce" back - from being quite literally at death's door on 23rd, he was off the ventilator on 25th and home on the 27th!