Last night, I was carrying my child to sleep. The lullaby song played for the millionth time in the darkness. That day I was tired. (Well, aren't we all.) But my left arm was beginning to ache even when I wasn't carrying my 20 pound little boy. But this was the homestretch to another long day. Normally, I'd be irritable at this point. Impatiently waiting for the boys to fall asleep so I could have some time with the wife or to myself, if our brains were still functioning.