SLEEP deprivation has got to be one of the biggest challenges of parenthood. Baby books and manuals are full of well-meaning advice on how to ensure youngsters and, just as importantly, mum and dad, sleep through the night.

Then, one day, after years of leaping up through the early hours, you crack it. No weeping, no wailing, no nappies to be changed, no bottles to be filled. Oh, the bliss of sinking into a deep, undisturbed sleep.

Enjoy it while it lasts. Because, once your little cherubs evolve into teenagers, the sleepless nights start all over again. And there is no parenting manual in the world that can easily guide you through this one.

My boys should know by now that, if they don’t return home when they say, I will be lying awake in the dark, convinced they must be lying dead in a ditch somewhere. This is what being a mother does to you.

Because once teenagers start to go out at night, there is so much to worry about. When they were younger, we kept them well away from the edge of the water because we could picture them falling in.

We scooped up tiny Lego bricks from the floor, because we anticipated they might put them in their mouths and choke. We wouldn’t let them go out on their bikes without a helmet, because we knew what could happen if they had a crash and banged their head on the pavement.

Following years of anticipating potential disaster, we mothers have become experts at seeing where everything can go wrong.

We try not to think about the fact our sons are heading off in cars with other teenagers, playing loud music and laughing and chatting distractedly as they travel along winding roads in the dark. We desperately push to the back of our minds all those stories in the newspapers about alcohol-fuelled arguments in nightclubs and knives being pulled out during a minor scuffle in a kebab shop.

But lying in bed, in the still, quiet darkness, what else is there to do but catastrophize? It is impossible to sleep until they are back, safe in their beds.

So when the 19-year-old and the 17- year-old still hadn’t arrived home by the early hours of last Sunday morning, my mind was in overdrive. Both at different parties in town, they were supposed to be sharing a taxi back together.

But they didn’t return. There were no texts or calls. By 5.45am I started calling them on their mobiles. No answer.

There was thick snow outside.

By now I was trying not to dwell on the thought that they might be lying, cold, in a ditch under several feet of snow. But soon my fitful, sleep-deprived brain was conjuring up a series of hideous images involving everything from blood stained knives to mangled cars.

By the time the 17-year-old returned my frantic calls, I was convinced he was lying in a gutter with a knife in his back. “But I just stayed over at Sam’s,” he said casually, like it wasn’t a problem. “I didn’t have a phone signal, so I couldn’t call.” The gutter and the knife simply hadn’t occurred to him.

Around 8am, the 19-year-old called to say he had stayed at a friend’s.

“But didn’t you realise, I thought you were lying in a ditch, under several feet of snow?” I wailed.

“Sorry, I would have texted you, but my phone ran out of charge. I couldn’t access your mobile number.

By the time I decided to stay, it was too late to call you on the landline.”

And then he added, ever so thoughtfully: “It was four in the morning. I didn’t want to wake you up...”

ILOVE having my big boys home from university. But there are some things, like the mess, the noise, and the constant devouring of huge volumes of food, which all take time to adapt to again. My sister sensed as much when she read my 19-year-old’s Facebook status the other day. “I have not been home 24 hours and my mum is already closing doors on me because my laugh, apparently, annoys her so much.” In my defence, it is loud and hammy and it annoys everyone else in the house too. But it is nowhere near as bad as comic Jimmy Carr’s. Listen to it on YouTube. I don’t know how his mum puts up with him.