The Dragons number eight had just finished lunch at a family barbecue near Bath.
But one “freak” moment later – as he dived into the shallow end of a pool thinking it was the deep end – left the 28-year-old with a broken neck.
Jackson was told at the time he may not walk again.
Now, after more than 11 weeks of gruelling recovery and rehabilitation at three different hospitals, he will be allowed to go home.
He is still in a wheelchair and he will never play rugby again. But he has regained significant movement in his arms and legs.
And, having floated in the pool immediately after the incident only able to move his eyes and mouth, Jackson is grateful simply to have made so much progress.
Jackson’s ability to candidly recount the incident that altered his life forever has helped him in his recovery.
“They had a pool at their house and I hadn’t been in it before,” said Jackson.
“I walked over and they had this water feature off the side of the rock face next to the pool.
“I jumped and dived in where the waterfall went into the pool and went straight to the bottom and whacked my head.
“It turned out to be only four feet deep. I thought it was about 10 feet.
“I remember thinking ‘that hurt’ and couldn’t stand up.
“I had some power in my right side so was able to pull myself up above the water and just said ‘help’ before sinking back down.
“I had this weird feeling, an ‘is this it?’ sort of moment, but luckily I had some friends in the pool and my dad who knew I wasn’t messing around.
“If it had been a group of lads on holiday maybe they would have jumped on top of me.
“My dad is a retired doctor and knew straightaway there was something wrong with my neck.
“I also had a cut down the middle of my head so there was a lot of blood over my face.
“He held my head steady, floated me to the pool edge and waited for the ambulance. He was a good, calming influence.
“I had movement on my right side but as I lay there, slowly everything disappeared until it was just my mouth and eyes working which was scary.
“I remember virtually everything. I wasn’t panicking or scared.
“I knew I had done something bad but was still trying to crack jokes with my mate Daf.
“I am not sure if it was shock but there was a weird sense of calm, while everyone’s panicking around you.”
Right time, right place?
Jackson believes his father’s composure and medical training, plus the close proximity of a specialist hospital were major factors in his recovery.
“50% of damage in spinal-cord injuries happen after the event from being moved around,” he said.
“I was fortunate my dad was there and I could float in a pool. They floated the spinal board underneath me and picked me out.
“I feel lucky not to have more damage. I was close to one of the leading spinal centres in the UK in Southmead in Bristol, in terms of acute surgery.
“They took one look at the MRI scans and rushed me straight into surgery.
“I managed to get operated on within seven to eight hours, another big factor in spinal injuries.”
Realising the damage
Jackson had fractured and dislocated the C6 and C7 vertebrae and shattered the disc between them.
His spinal cord was impacted and partially crushed, resulting in damage, swelling and spinal shock.
Jackson was initially told he may never walk again.
“They told me I might not get any movement back,” said Jackson.
“Before I went into the operation, the surgeon said things that could happen, one of them being death, which was interesting.
“My fiancee, mum and stepmum were in the waiting room with my dad. They were told this was a serious operation and a chance I might not make it through.
“My dad told them not to panic because he knew doctors tend to be cautious and always give you worst-case scenarios.”
Jackson had no initial movement from the chest down and admitted he endured tough times before the shoots of recovery.
“It was difficult, at the start, usually at night when none of your family and friends are there and you are in intensive care, it’s 24/7,” said Jackson.
“I couldn’t swallow so I was hardly sleeping. I couldn’t cough and someone had to come in with a suction tube.
“You think how much worse can it get but as time moves on, you start to progress.
“I was hoping to get arm movement back to be independent. I never wanted to be a hassle.”
Jackson played for Bath, Wasps, London Welsh and the Dragons and was a bullocking, ball-carrying back-rower, who at 6ft 4in and 17 stone powered through opposition defences.
Now he was revelling in the slightest physical activity.
“My fingers started moving first,” said Jackson.
“The biggest elation was seeing my right toe wiggle after weeks of staring at my foot trying but nothing happening.
“That first moment I saw the signal from my brain going to my foot was big because you had something to work with.
“Little wins like that have been happening over the last eight weeks, which are bigger than any league title.
“I have been living amazing moments with tears of joy over the last three months. You don’t get that in normal life.”
Reliving his story
Jackson has been charting his recovery in a social media blog which has attracted the attention of medical professions, Paralympians and other people in his situation.
“I was keeping a personal diary as soon as I could use my hands and found it therapeutic,” said Jackson.
“I was persuaded by friends to make it public and thought it could help a couple of people.
“In a couple of weeks it went crazy, going around different hospitals with nurses and physios reading it.
“I had some great feedback and I am now in touch with some Paralympian gold medallists and amazing people in my situation.
“You can’t get much better input from people who have been through it themselves.
“I think I have helped a few people but if anything it has helped me massively. Now I just have to keep it going.”
Jackson says his recovery has been helped by the support network of family, friends and fiancee Lois Rideout, who plays netball for Cardiff-based Celtic Dragons.
“They have been unbelievable,” said Jackson.
“You don’t realise until you are in a situation like this about how good a network of people you have.
“My fiancee Lois has been a saint, she has been in every day. She is basically my own private physio now because she has sat in on all the sessions.
“My family have been brilliant and old school friends are always visiting me. I am lucky because some people don’t have that.”
What next after rugby?
“I have been obviously told I am not going to play professional rugby again,” said Jackson.
“If someone had said that to me before, that would have been terrible. It was all I had ever known, what was I going to do?
“I am getting my head around things but there are more important things, like trying to be able to walk again.
“Now the boys are back pre-season and I am not going back into training, it’s starting to hit home.
“The Dragons have been supportive and the rugby community’s response has been unbelievable. I have had messages from all over the world which is humbling. People who have I never met or only played against once or twice.”
Dealing with the financial cost
Jackson admitted the question of insurance was unresolved and his plans on life after rugby yet to be formulated.
He has been helped by the Restart programme, part of the Rugby Players’ Association, which has granted him money for rehabilitation to help bridge the financial gap.
The Matt Hampson Foundation – started by the former Leicester prop who was left paralysed after an injury – is also helping by paying for his wheelchair.
“I haven’t moved on in my head that far,” said Jackson.
“I did a degree while I was playing and am doing a Masters, so was getting things in motion.
“This happens and everything goes out the window.
“I want to help the charities that have supported me, to give something back.
“When the money runs out and I have to go back to work, I will cross that bridge then.
“I don’t know how long this journey will be. But it’s going to be expensive.”
Moving out of hospital
Jackson has been latterly a patient in Salisbury District Hospital, where his recovery has been aided by Horatio’s Garden – a charity that creates picturesque and accessible gardens in NHS spinal injury centres – which has added mental stimulation to his physical recovery.
On Tuesday, 27 June, he was given the all-clear to leave hospital to live with his father and stepmum in Bath, with the Cardiff home he shares with his fiancee unsuitable and unable to be modified for his needs.
Still in a wheelchair, Jackson hopes to be walking again soon.
“My left side is more damaged,” he explained.
“I have good movement in my arms. My left hand started moving three weeks ago but there is no strength.
“My right leg is good. In my left leg I have power to push and can extend it but have no strength in my ankle. I can’t pick up my foot, which is stopping me walking.
“So things are moving but have slowed down. Changes are weekly rather than daily but I am hopeful I can get it all back.
“If someone had given me this diagnosis in week one where I had no movement in all four limbs, I would have bitten their hand off.
“I have more back then I could have ever prayed for.”
Setting tough targets
That is not to suggest Jackson is content with his current state. He wants more.
“I want to be able to challenge myself physically again and not just as someone with a spinal injury,” said Jackson,
“I want to take my mates for a walk so they can’t keep up with me.
“My goal is to be back fit and healthy and be able to do what I want to.”
Jackson insists there are no demons about returning to water, with hydrotherapy proving a key part of his rehabilitation.
He has even targeted going back to the pool “that did this to me, getting my own back and kicking a few tiles”.
“I am comfortable thinking about the incident,” said Jackson.
“There is no-one to blame. I don’t blame myself. It was a freak accident, I just wasn’t concentrating. I don’t blame anyone else. I wasn’t drunk.
“All of a sudden things happen. You can’t plan for them and they come from nowhere.
“But I will definitely be more cautious about going head first into anywhere.”
Never feared the worst
Jackson has insisted he never thought about the worst-case scenario.
“At no point did it cross my mind I could have died,” said Jackson.
“In my head I wasn’t in a situation where I was fighting for my life. I was fighting to walk again.
“It never crossed my mind I could have been stuck at the bottom of that pool, because that was not a position I was in. It’s not worth thinking about.
“I am lucky perhaps because I am a bit blase, which has helped me in this situation.
“Being in hospital, you see there are people in far worse situations living amazing lives.
“I have no right to feel upset or sorry for myself. It’s just another injury I am rehabbing from, that’s how I am looking at it.
“My life has changed completely but I am excited about what the future holds. It’s not scaring me.
“Time will tell how much I get better.
“Even if it does not get any better than this, which I am sure it will, I will be fine.”
By Gareth Griffiths
BBC Wales Sport