Has he always done this, or only after the A? Does it matter what time of the day it is,eg. morning vs night? Does he fall asleep at other times, eg. watching TV?
I don't know, I'm sure others will be along to help you better.
I know my H couldn't keep an erection all the time with me after dday, something he has never done before. He also can sleep anytime, anywhere. He was diagnosed as having sleep apenia (sp) and thus doesn't sleep well at night, so he is tired a lot.
Does he say anything else besides I am tired?