http://fitbottomedmamas.com/2013/02/tale-as-old-as-time-parental-exhaustion-and-coping-strategies/
This is just another reason I think it's good to have your kids close together-- you're awake for like 3 years straight, but then you finally, finally, get some rest. It's actually harder when you get a break in the middle but then have to do it all over after remembering what true sleep really feels like ;)