The first night back from the hospital, I tried not to cry. In the dark, I squinted at the wall clock. The thick black hand hovered around the three. I lay propped up against pillows and towels. My baby’s body was hot and furious. Her little head fit in the palm of my hand. I was convinced I was holding her wrong. That if I could do it right, she would feed and rest and grow up healthy and strong. But my grip felt weak and wobbly. This might have been because I’d had a C-section and they’d cut through several layers of my flesh. Or because I am generally clumsy. She wept and wept.

I thought about how much I loved her and how uncertain I had been about becoming a mother. Achy, bloated and exhausted, I was not sure I’d made the right choice. This had nothing to do with her and everything to do with me. I did not feel cut out for the task of mothering. I had the support of my family. My partner’s work had given him generous paid leave. Entering parenthood, I had as much safety and stability as anyone could. Despite all these advantages, I was failing to give my daughter the two things she needed: food and sleep.

My nipples were cracked and bleeding. When her small mouth latched, I wondered if she could taste the blood. Earlier in the evening, I had fondly called her “our little vampire”. Isn’t it strange, I thought, that milk is just blood transformed by the body? But that commonplace miracle was faltering. My milk was behind schedule. I was struggling to make enough to meet her needs. I had been told to persevere until it improved. I’m sorry, I thought. I’m so, so sorry.

I had tried to prepare. I had read about the pros and cons of breastfeeding, of dummies, of rockers, and of co-sleeping – about which I’d been unsure. My understanding was that co-sleeping had risks but that done properly it could be safe. We had bought a bassinet, but I was open to the idea of bed-sharing. It hadn’t occurred to me we might just be co-crying instead.

From the darkness a memory came seeping out. For me, there is a point when I’m so tired that thoughts and memories become extremely vivid, almost superimposed over what is actually happening, like waking dreams. I saw my mother, lying in bed next to me, her hair falling over her face. I could hear her sigh and see the way her eyebrows drew together as she slept, as if puzzling through a point.

This memory came not from childhood but from a time in my early 20s. I had relapsed into the depression that haunted my teenage years. Although I had tried to hide its return, I had been found out. And my mother decided to move into my bed.

She didn’t offer me a choice about it, but nor did I argue. I wasn’t up to resisting. But I remember thinking it was ridiculous. What was sleeping in my bed supposed to do? For years I had been plagued by an insomnia that would in part inspire my third novel, The Sleep Watcher. I’d spent long nights wandering my childhood home in the isolation of the dark. In my 20s, I still struggled with sleep. So I lay awake and watched my mother snooze. She couldn’t make me less sad. She couldn’t grant me sleep. She couldn’t even keep me safe – I was an adult, and in the daylight hours I had to go and be alone in the world. Still, she slept there until she thought I was well enough to spend nights by myself.

As this memory played out, I realised that my mother and I had been co-sleeping. In the face of not being able to do anything else for her adult child, she had chosen to be there through the night. And it did help, if not in any obvious or instantaneous way. Her body had anchored me in the knowledge I was loved. The proponents of co-sleeping argue that separation occurs naturally – there’s no way you’ll end up in the same bed with your adult child. But I guess there are exceptions.

Steeped in darkness, I promised my daughter: I will do everything I can to soothe your pains and solve your sorrows. And if all else fails, I will be there as long as you need me.

In the months since, there have been easier and harder nights. There have been times when I have questioned my worth and strength. I’d be lying if I claimed that in that one moment I solved parenthood. But when I feel overwhelmed I remember that night and my promise to her. And the shame I feel about not being a good enough parent eases, because I know that at least I can do this for her.

Lately, she has slept peacefully in her crib. But friends warn me this could change any day. I know the world may have new sorrows in store for her. Sadly, a mother’s kiss can’t cure every wound. Co-sleeping did not cure my depression. Still, it mattered. I didn’t understand what my mother was doing for me until almost a decade later. But her love gave me a safe place inside which to struggle. I will try to do that for my own child. I hope that even when my efforts have no visible effect, the love may soak into my daughter’s skin and fortify her in some future year.

The Sleep Watcher by Rowan Hisayo Buchanan is out now (Sceptre). To order a copy, go to the Guardian bookshop.