Imagine your young daughter had been knocked down, suffered horrific, life-threatening injuries, required an air ambulance and emergency surgery and spent weeks in hospital afterwards.
Now imagine that you're the one who put her there.
Mother-of-two Mary McDonnell from Portaferry doesn't have to imagine it. She's been living with relentless flashbacks of this horrific incident for the last six months.
That's because the quad bike 15-year-old Ellie McDonnell was riding was involved in a catastrophic collision with her mum's 4x4 on a blind bend on a lane leading to the family home.
There followed indescribable, terrifying trauma - physical for accomplished horse rider Ellie, but psychological for 52-year-old Mary, wife of a dairy farmer on the Ards Peninsula.
Now, however, both mother and daughter are well into the recovery process following last summer's devastating accident.
Ellie - who'd just been picked to ride in the Northern Ireland team in a competition in Wales at the time of the crash - is back riding horses, and her relieved mother is finally ready to talk about the morning when disaster came calling.
It was around 11.30am on July 23, 2019 when Ellie was thrown from the quad, crashed into the windscreen of the car, and landed in a ditch at the side of the lane leading to the farm.
"I saw her in the last two or three seconds... and I tried to drive into the hedge but a telegraph pole stopped me and Ellie hit the front of the jeep with the quad," Mary said.
"Then she somersaulted through the air, hit the windscreen with her head and then somersaulted behind the jeep and landed on the grass verge in the lane. The bang was just deathly."
She added: "That bang was horrendous. If I'm going along doing something in the house I still get that flashback.
"I have to stop myself thinking because I would just go mad. I blank it out because Ellie is doing so well and we've got over it, but we'll never forget it."
Mary recalled jumping out of the jeep and running to Ellie to find "blood everywhere". "The blood was in her mouth and she was drifting away and there was a slow gurgle that sounded like she was taking her last breath," she said.
"I was on my knees. I pulled her on to her side and the blood started running out of her mouth and I screamed at her to wake up. I was screaming at her not to die, to stay with me..."
With her "hands clabbered in blood", Mary told how she ran to the car to get her mobile phone to call for help.
She tried to reach her husband Peter who didn't answer so she called her neighbour Pauline and told her to get Peter because "Ellie is dying".
"I knew I needed to get some help before I called the emergency services... then, after I dialled 999, I told them I needed an air ambulance," Mary said.
"Ellie had serious head injuries, she was open from the front to the back and she was going in and out of consciousness."
Mary's husband, neighbour and brother-in-law Kieran arrived and helped calm the teenager "because she was screaming and fighting to get up" while they waited for help to arrive.
Ellie, it later emerged, had sustained broken arms, legs, eye sockets, cheeks and teeth, and had severe swelling on her brain.
Shortly after their arrival, the Air Ambulance NI medical team put her into an induced coma to protect her brain and then she was transported to the Royal Victoria Hospital in Belfast.
Mary and Peter (52) went by car to the hospital where Ellie spent the following eight weeks, two of them in a coma. Son Max (11) stayed with relatives. With Ellie in surgery, Mr and Mrs McDonnell were told to prepare for the worst as the extent of her injuries left doctors unsure of her survival, never mind whether she'd ever be able to walk or talk again.
"We walked past her bed; we didn't recognise Ellie, who was unconscious, at first," Mary said of their post-operation reunion.
"Her head was double the size it should be, she was like an alien. There were so many tubes, computers, monitors and breathing machines around her.
"She didn't look like a wee girl. She looked like an old woman. She was hanging by a thread."
Ellie was "so close to death" that neither Mary or Peter left her hospital bedside during those long, worrying weeks.
Mary recalled the first thing Ellie - who initially thought she'd sustained her injuries falling off her horse Olaf - said to her when she first came round.
"She smiled, and when I asked her how she was feeling she replied: 'I'm feeling rather average' - and she's never used that word [average] in her life," Mary said.
"The consultants themselves can't explain her recovery. They honestly thought she was going to die and they told me to prepare myself because she was so ill."
Ellie, a pupil at Down High School, was finally discharged from hospital on September 20 last year, and her almost miraculous recovery has helped her mum overcome her guilt.
"That night [of the accident] I thought, how am I ever going to breathe again or live if Ellie doesn't survive?" Mary recalled.
"I couldn't have survived without her. We're a very close family and we do everything together. It was an awful situation to be in. You run into your daughter and she's lying dying in front of you."
But Mary also said she was "glad it was me who hit her on the lane and not somebody else".
"I did what I did very quickly because I was damn sure I was going to do whatever I could to keep her alive," she added.
"Who knows? Somebody else could have frozen. Normally I'm really squeamish around blood. I'd go weak at the knees.
"But that day I didn't. I've no idea why. Maybe the mother's instinct kicked in..."
Air Ambulance NI depends on public donations - it costs £5,500 per day to keep the helicopter in the sky. Air Ambulance NI is a charity that provides the Helicopter Emergency Medical Service (HEMS) for Northern Ireland, together with partners at the Northern Ireland Ambulance Service (NIAS). From its base near Lisburn, the air ambulance can reach any part of NI in around 25 minutes. For information visit Air Ambulance NI's Facebook page.