I did a long bedside vigil on a paediatric intensive-care unit 12 years ago. A cold sweat of terror defines that time for me, along with mad-eyed private bargaining -- "please, whichever god is listening, make my child okay. I'll give you my legs/eyes/arms if you make my child get better" -- the sort of deranged thing that some of you will know.
Three mornings in, when my fear was oscillating far beyond my ability to control it and I'd forgotten how to sleep, one of the nurses said, "There's someone here to see you. You can go and buzz her in."
I left my husband at the bedside and walked, unseeing, down the corridor. The door to the unit had a small, clear pane of glass. It framed the face of an old friend on the other side, who I believed to be in England. I buzzed her in, and charged her like a clumsy dog. She held me hard and I was too distraught to smile or thank her for coming.
It took weeks for my child to stabilise, so another old friend flew over and listened while, corroded by worry from the inside out, I gave voice to my fear with the same kind of insistence as a wasp trapped in a can. And like a wasp trapped in a can, she told me over and over again that everything would be okay, which was the only thing I wanted to hear.
Eaten up by fear, I ate her up too, not even stopping in her fag breaks and, with her, that's saying something.
One of these friends has the temper of a crazed despot and the other one eats much too loudly -- chomps, in fact, like my daughters' old pony Lancelot. And she votes Conservative. I couldn't care less about the temper, chomping or politics, and my annoying traits don't appear to bother them too much.
That's friends for you, though. Real ones, anyway.
Like many other women, my own benchmark for friendship has been forged over a lifetime and in some stark circumstances -- I know who passed my wasp-in-a-can test and I know who failed. But reciprocity is vital. You need to pass your friend's wasp-in-a-can test, too, in your fag break.
Being there for each other no matter what -- this is the bedrock of friendship, but it's about more than this too; being understood without having to explain too much is another common denominator for true-blue friendship, and a shared sense of humour is important.
Having a good friend is about straightforward things, such as not being able to help smiling when you see her.
Liking, in other words, is essential.
However, friendship is not a static thing. Circumstances can alter the alchemy of friendship and knock it off balance, destabilise and fragment it.
Why, once in a while, does the spontaneous smiling start to feel more forced and the liking fade? What happens when a friendship implodes? How painful is it to fall from grace or call time on a meaningful friendship?
According to the results of several research studies, the fallout from falling out hurts a lot. Some studies have found that the pain of ending a friendship rivals the emotional trauma of a romantic split in intensity. Significantly, the pain can endure for longer. Why is this?
Stephanie (46) has had the same eclectic group of friends for many years, one of whom she met when she was five years old in the schoolyard. She remembers linking fingers with her at different times throughout their national school years and chanting that old playground skipping rhyme, "Make friends, make friends, never, never break friends, if you ever break friends, make friends again."
She says: "This is the female ideal of friendship -- that you'll always support each other in a resilient bond, and for 30 years we had the ideal."
At this point, they severed all ties, which she confesses is still deeply saddening to her, especially when she knows there is no way back. Theirs was a close friendship: "Everything was there that needed to be there; she understood me, there was a shared history which meant she knew where I was coming from and we never had to second-guess each other."
Stephanie explains that they also allowed each other elbow room to forge other sustaining friendships over the years and that petty jealousies surrounding this issue were never a problem -- "It was a mature friendship," she says, "in every sense of the word".
I wonder what on earth could shake such solid foundations. "Nothing dramatic," she laughs. "She didn't run off with my husband; it was more subtle than that, it was a cumulative thing."
She describes how the reciprocity, something she considers fundamental to abiding friendship, simply became more and more skewed. "Look," she says, "I was clear-eyed about her. I knew she had a complicated relationship with alcohol and this became more evident as time went on. When she broke up with her husband, the drinking escalated and she started leaning on me heavily, but, also, she began doing things I honestly didn't like."
When she started dating married men and drinking to excess around her baby, Stephanie was unnerved. "I tried to support her but, after three years, three years started to feel like a long time." She explains that there are times in a friendship where one person's needs outweigh the other's, but over time, this needs to balance out.
"I knew that the drinking was going to be ongoing and there was never going to be room for me to take as well as give and, frankly, I was exhausted," she says.
Though certain she made the right decision, Stephanie remains sad that her friend is no longer in her life. "I still miss her," she says. "I miss knowing that she's there. It was an extra dimension that survived all the momentous changes in our lives -- births, deaths, marriages -- she was a background constant and now that's gone. I just miss her."
To consider a rapprochement, Stephanie would need her friend to change "but from what I've heard through a mutual acquaintance, she's still drinking, still doing crazy stuff and still resolute about it".
Irene S Levine, a clinical psychiatrist and professor at NYU Medical School, affirms that negotiating the end of female friendships can be intensely painful, yet it rarely garners the same social support as a romantic break-up. In her research study, which involved 1,500 women aged from seven to 70, she found that many older women still nursed acute distress over friendships that had fallen apart 20 or more years ago.
"A broken friendship is a taboo subject that women don't usually talk about," explains Levine. "It's embarrassing and associated with stigma. We don't even have a vocabulary for why friendships fall apart or a roadmap for what happens when they do."
The search for a life-long bosom buddy begins very early, often starting in the school playground, a variably toxic arena for a search of such emotional delicacy. At 10, we read books such as 'Anne of Green Gables', in which the virtues of indestructible female friendships are extolled. Watching TV programmes such as 'Little House on the Prairie', we shudder at Nellie Olesen, the archetypal frenemy, and identify with Laura, the gal-pal we long for.
The promise of the friendship ideal is all around us. We absorb it as if by osmosis. No wonder it hurts when it ends. As Levine says, "Women want to have a best friend and be a best friend. But, over time, the realisation hits that they need different friends for different reasons. It's unrealistic to expect any one person to meet all your needs".
I think this, like reciprocity, loyalty and understanding, is the crux of friendship. What I've learned, through one friendship that fractured in my 20s and a handful of sturdy others, is that expecting any one of my few close female friends to fulfil all my needs is setting the bar for friendship too high.
Friendship can be a casualty of the emotional revolutions in women's lives -- graduation, children, marriage, widowhood, divorce -- but real friendships can survive these upheavals and become enriched by them.
These friends are the ones I treasure.