The X-Files star began struggling with perimenopause, the hormone change prior to full menopause, two years ago, when the mother-of-three suddenly found herself unable to juggle her work and home responsibilities as she had been doing for ages.

"It was at the point that I felt like my life was falling apart around me that I started to ask what could be going on internally, and friends suggested it might be hormonal," the 48-year-old shares in an interview for Lena Dunham's Lenny Letter.

"I was used to being able to balance a lot of things, and all of a sudden I felt like I could handle nothing. I felt completely overwhelmed. When I talked to the menopause specialist, she said that she often gets phone calls from female CEOs screaming down the phone, 'I need help now! I am losing my mind!' And that's completely right. I felt like somebody else had taken over my brain."

Gillian drew from her own experiences for her new book, We: A Manifesto for Women Everywhere, written with her journalist friend Jennifer Nadel, in which they encourage others to share their experiences more openly to help spread awareness about perimenopause and the accompanying mental health symptoms such as anxiety, depression, hot flashes and fatigue.

"How wonderful would it be if we could get to a place where we are able to have these conversations openly and without shame?" she asks. "Admit, freely, that this is what's going on. So we don't feel like we're going mad or insane or alone in any of the symptoms we are having."

And Gillian reveals she has great admiration for Angelina Jolie, who spoke openly about going through early menopause after undergoing preventative cancer surgery in 2015.

"When Angelina Jolie made the very, very courageous decision to have both her breasts and her ovaries removed because of genetically being at risk for breast and ovarian cancer, many of the comments (aside from admiration for her decision to go public with a very private matter) were around the concern that it might throw her into early menopause," Gillian explains. "Then she became vocal about being in menopause and pushed back against the narrative that ageing is bad. It's a step that more of us in the public eye need to take in order to shake the shame around it."

She adds, "Perimenopause and menopause should be treated as the rites of passage that they are. If not celebrated, then at least accepted and acknowledged and honoured."