Quickstart Autism, a local charity, does draws every year to give parents a chance to have a night or two away from their children and give themselves a chance for a break. The hotel rooms are donated by local hotels and Quickstart usually provides some funding for childcare and meals.
You can apply on Quickstart's website under Info and Resources --> Respite.
It may not sound like a lot, especially when you're overwhelmed, but I've found that even one night away with a solid sleep can make a big difference.
Parents are responsible for finding their own childcare for their kids. There are a couple of different places which can help with that, if you don't already have someone. Andrew Fleck offers short term child care, including overnight, for children with special needs. Autism Ontario has a database of respite workers and FASD has a list of respite services in Ottawa.