My wife couldn't breastfeed in the sleeping position. We had to prop her back at an angle with pillows to at least rest while she did. She didn't have a good experience after the birth of our two sons, but she'd keep comments like that to herself. She only revealed this after she completed as much as she could of breastfeeding.
You could see it in her face, though. I couldn't drag it out of her at the time, and I didn't want to do so. I just supported her whenever she needed me.