Have you found out about your windows of tolerance yet: those moments when you feel fully capable of handling any stress life throws at you? Our tolerance shrinks and expands to suit our needs, but these “windows of tolerance” are a funny thing for women, as I have just discovered, because they unexpectedly disappear when we hit midlife. Sometimes they’re just tiny cracks in the glass and yet you feel you can’t tolerate any stress ever again. It’s a contrary conundrum, as you’d expect life experience and maturity would increase your ability to cope, wouldn’t you?

However, for an army of midlife women the turmoil of this life stage often inexplicably whips away our ability to deal with difficult situations overnight, from the simplest family problems to the biggest career dilemmas. Any amount of stress seems to overwhelm us. I know this not just because I am a woman in my 50s and I’ve been through it, but because I have interviewed many women over the past four years in my role as co-host of the Postcards from Midlife podcast and author of What’s Wrong With me? 101 Things Midlife Women Need to Know.

Again and again, women over the age of 40 told me they, too, had been ambushed by a sudden inability to deal with stress. Yet it’s something we rarely talk about. I mean, I forgot which side of the road to drive on at one point in my late 40s I felt so demented with stress (not something you really want to talk about out loud). A 48-year-old woman told me she once flew jumbo jets long haul and yet the day I interviewed her she’d become so stressed out reverse parking her small car she’d given up in floods of tears. “I don’t tell anyone I used to be a pilot nowadays,” she added. “They wouldn’t believe me.” With her windows of tolerance completely shut, she’d lost all that confidence born a groundbreaking career alongside bringing up a family.

I first learned the phrase “windows of tolerance” from therapist Julia Samuel. She explained that throughout life we adapt as our “windows” get bigger or smaller to suit our needs, but in midlife, many of us seem to lose this ability to recognise what we can and cannot deal with and drown in the resulting stress. This is frustrating because, alongside this stress overload, we also stop sleeping in middle age. These changes may get in the way of our ability to work as efficiently as before, to maintain relationships, parent our kids patiently, look after our elderly parents’ affairs, and nurture our mental health. It is worth noting that the highest rate of suicide for women in the UK is between the ages of 45 and 49.

So, what’s going on and why does this unwelcome inability to cope with stress hit many of us out of the blue? According to the experts I interviewed for my book, it all starts with the perimenopause: the 10 or so years before the menopause, which kicks in at around the age of 51 in the UK. During that time your hormones – oestrogen, progesterone and testosterone – fluctuate and eventually decline. Oestrogen is like petrol for the female body. We have oestrogen receptors everywhere, making sure we function well, and when this hormone fluctuates and dips as we age it can prompt more than 40 symptoms of perimenopause. Symptoms range from insomnia and depression to tinnitus and aching joints. Losing oestrogen from our brain scrambles our neurology (oestrogen controls the neurotransmitter serotonin, which regulates mood).

I went from coping with a high-flying job editing ELLE magazine, travelling the world and writing a book, then launching a podcast and co-parenting four children to having panic attacks about the journey to work. I was getting up at 5am to tackle a to-do list I could no longer cope with. This new “incompetence”, as I saw it, was a surprise. It shook my sense of identity. I was also regularly waking up screaming with terror after gory, upsetting nightmares and covered in so much sweat it looked like I’d swum the Channel in my PJs.

The decrease in the hormone progesterone is known to specifically affect our sleep patterns. And as we now know from the work of experts, such as Professor Matthew Walker, good sleep is vital to our health. A lack of it is linked to increases in heart disease and dementia (the leading cause of death in women in the UK in 2022). Women are twice as likely to be hit by insomnia as men. In 2017, a quarter of middle-aged women in the US told a CNN survey they had hormone-related sleep issues.

I was so distressed at losing my Olympic ability to sleep at 47, an ability that had only wobbled once before, during the baby years with my four kids, that I commissioned a survey into it for the newspaper I was working on in 2019. Women who responded told us they found stress a huge reason for losing sleep in midlife, with 52% saying that they slept poorly, rising to 65% for the 55-64 age group. And in a cruel twist of medical fate, poor sleep exacerbates the symptoms of perimenopause. When American writer Ada Calhoun interviewed more than 2,000 women for her book Why We Can’t Sleep: Women’s New Midlife Crisis in 2020, it was the overwhelming theme and made headlines globally.

I was offered antidepressants by my GP when I first told him what I was going through but, instinctively, I knew they weren’t right for me. I put my journalist hat on to interview the country’s leading menopause guru, Dr Louise Newson, because that’s what I felt was going on with me. She explained the hormonal changes and prescribed hormone replacement therapy, which eased my symptoms within a couple of weeks.

I felt as if I had unravelled and HRT put me back together again: I could sleep and my brain fog lifted, but I also began to realise that my window of tolerance for stress had narrowed. Recognising this had happened actually wasn’t a bad thing for a mildly burnt-out Gen X woman; knowing about it meant I could manage it better.

I felt overwhelmed by the emotional aspects of midlife and had to learn to start saying no to things. My shifting identity made me question how I wanted to live my life. I felt as if I was “landing” after one adventure and taking stock before looking forward to a new one. And as I did my research, I realised how powerful this transition could be, if only we knew it was coming. At the end of last year, I found myself back in a particularly busy period of work. The to-do list was huge, my second child had left for uni, my youngest was moving up to a junior school, my dad wasn’t well, I’d developed a lump in my breast, which thankfully checked out as fine, but added to the stress. The occasional sleepless night returned. One Sunday, I had to interview Davina McCall and Dr Naomi Potter on stage about their book, Menopausing, at the Cheltenham literature festival. That night as I slept in the hotel room, I had felt the weight of someone climb on top of me in bed and pin me down with their hands. I was terrified. A few seconds later the weight disappeared. There had been no one in the room: what I had experienced was a parasomnia, or sleep disorder.

Parasomnias are stress-induced according to the leading expert on night terrors, Dr Alice Vernon. Apparently the brain takes over during that state between waking and sleeping to stop your body acting out your nightmares. She tells me that, anecdotally, it does seem to happen more to women and especially during hormonal fluctuations. I’d never had one before, even during my most stressful times at work. The lesson I learned from it was that it is vital for women to take control of stress as they age, to manage it well and develop coping strategies.

There is a sexist school of thought where older women talking about physical and mental weaknesses makes us seem unfit for work. There is this idea that we are past our sell-by date. That’s why the Boomer generation before us kept quiet. But this is the wrong way to approach midlife. Preparation is key and I see many women of my generation working at the highest level of their industry while coping with these symptoms. Imagine if they had known what was coming and been ready for it. They would be even more unstoppable.

If you are over 40, utterly overwhelmed, stressed and can’t sleep, and everything makes you angry or tearful, you could be perimenopausal. Help is out there at last, but you must ask for it, and you must talk about it because we’re all on this midlife adventure together. It’s less stressful that way.

What’s Wrong With Me?: 101 Things Midlife Women Need to Know by Lorraine Candy is published by 4th Estate at £16.99. Buy it for £14.95 at guardianbookshop.com