oh becky - you poor thing but you have done SO well to get this far. you have had over a weeks worth of 'good' sleeps. this one night doesn't mean it's coming back. i promise it's just a blip.
one trick my CBT person told me is whenever you have intrusive catastrophising thoughts like, 'i've had one bad nights sleep, tonight is going to be even worse, i'm going to have a breakdown, i can't look after the children' then you need to stop them in their tracks.
the way she taught me to do this is to listen to every little sound around you. so when your brain begins the cycle of thoughts just tune your brain into what you can hear. if it's someone talking to you then focus on every word they're saying, if it's the TV likewise, if you're loading the dishwasher then listen and almost mentally name the sounds you can hear as the plates go in etc. you get the idea.
it does work but you need to be really strict with yourself because at the beginning your brain will do anything to get to the anxiety causing thoughts. plus it's even more difficult to do when you're tired. but once you've trained your brain then it can work even when you're really stressed.
i had to do it yesterday as we went to brighton for the day and the crowds were making me feel anxious. but by just tuning into all the sounds around me and naming them it took my mind away from the anxiety causing thoughts.
we seem to be on a similar path with our pnd and insomnia issues but i'm a few months along from you. take it from me, you WILL get better and this is the home straight now but you've just taken a little pit stop!
keep in touch today and i'll keep you going with positive thoughts.
xxx