I didn't know it was possible to switch off to the extent that you can sleep through your baby crying.
I wake the instant any one of my 3 start crying and go straight into them - it seems as if I am on call 24/7 in a very light and non-restful sleep. DH on the other hand doesn't hear a thing. I have had nights where DD was crying for a feed, DS1 puked everywhere and the DS2 pulled his nappy off and pooed everywhere, DH didn't even stir.
I am insanely envious of the ability to totally switch off. Can you? If you can, what's your secret?