"I felt like a zombie. I couldn't access my heart. I couldn't access my emotions. I couldn't connect," Paltrow, now 38, says in the February issue of Good Housekeeping.
"It was terrible, it was the exact opposite of what had happened when Apple was born. With her, I was on cloud nine. I couldn't believe it wasn't the same. I just thought it meant I was a terrible mother and a terrible person."
It was Paltrow's husband, Coldplay frontman Chris Martin, who first thought she might be suffering from postpartum depression.
"About four months into it, Chris came to me and said, 'Something's wrong. Something's wrong,' " Paltrow recalls. "I kept saying, 'No, no, I'm fine.' But Chris identified it, and that sort of burst the bubble."
Paltrow says the hardest part was acknowledging the problem. "I thought postpartum depression meant you were sobbing every single day and incapable of looking after a child," she explains. "But there are different shades of it and depths of it, which is why I think it's so important for women to talk about it. It was a trying time. I felt like a failure."
With those dark days long behind her, Paltrow has rebooted her film career – and begun a musical one – with her role in Country Strong. Her husband, supportive as ever, helped her learn guitar for the part – which came as no surprise.
"I can depend on him," Paltrow says. "He makes me laugh. He's really appreciative of me. You know, he makes me feel special."
Although sometimes, she has to push him a little to talk about his feelings. "I definitely have to coax things out of him when we talk. You know, he's British, so it's a different lexicon totally," Paltrow says. "But you have to communicate. Otherwise there's no relationship."