First, try to relax. Your milk supply is probably up from a week of nursing. So, take a deep breath, look at photos of your child, imagine him/her nursing. And try again in 20 minutes. Drink more water. Also, follow the tips in this video:
http://newborns.stanford.edu/Breastfeeding/MaxProduction.html
It will come back. I promise. It's just your body not used to the pump after the break.