make a little 'crisis box' for these moments, put anything comforting in there - a cuddly toy? pics of children/loved ones, a favourite dvd, bubble bath, chocolate, religious texts? maybe print off any messages to you from here that have helped in the past, simple reminders like 'this too shall pass' (sorry for the cheesiness of this but have clung to such fragile hope in the past ), something soft and reassuring like a scarf, book with favourite paintings/photos in, one or two sleeping pills if you have them?
you could also add a list, with telephone numbers that can be called at any time such as samaritans, your crisis team if you have one, and maybe a to-do list, things to do that might get you through the moment without taxing your already stretched-to-breaking-point brain: sort beads into colours, cry/scream into a cushion, water your plants, post on mumsnet, cuddle/feed a pet if you have one (poss not goldfish), curl up in a fluffy blanket, go outside if the sun is shining - maybe others will have better ideas to add?