Darcy McQueeney's son was underwater for less than 30 seconds before he was pulled out by an adult.
He seemed fine following the accident and was talking and eating normally, but a few hours later he became unresponsive and his mum said he is "very lucky to be alive".
McQueeney shared the above photo on Facebook and Instagram.
"Please take a good look at this photo," McQueeney urged in the photo caption.
"This is my 3.5 year old laying unresponsive in a hospital bed less than six hours after jumping into the pool.
"He only went under for less than thirty seconds. He was being watched by two sober, conscientious adults who were both less than ten feet away in a gated pool. That is likely why he is alive, because he was grabbed out of the water quickly.
"However, that small blip of time was all it took for him to inhale water. The water he inhaled caused him to spike a fever, desat, and become unresponsive due to a possible seizure.
"He was talking and even eating after the incident, but went downhill hours later.
"Everyone who we met in the PICU [Paediatric Intensive Care Unit] remarked at how incredibly lucky he is to be alive.
"Not only because he didn't drown initially, but because he was at a gigantic risk for secondary drowning.
"Despite him being able to eat and talk and seeming like he was ok after the incident, he was NOT ok.
"Water safety should be a top priority for everyone. Do not ever leave children unattended near any source of water. Even following all of the rules, accidents happen. Even if they are acting ok after near drowning, please take them to the hospital.
"What if we had assumed he was ok and put him to bed? I don't know how to stress this enough.
"His PICU nurse asked us to please use our experience to spread awareness.
"My son shocked everyone by bouncing back at record speed and is okay, but he is fortunate. Please spread awareness about how important it is to take water safety seriously, including after care for near drowning."
"A small amount of fluid goes into the lungs and the lungs become ineffective," Mulligan explained.
"Following a near drowning incident, in which water has been inhaled, it is vital for parents to monitor their child for at least five hours
"We're in the process of reviewing the research into dry drowning, so we can raise awareness of it, as currently there isn't enough understanding of the condition and that is why we end up with these dramatic situations."
So what is dry drowning?
"A small amount of fluid goes into the lungs and after a period of time the lungs become ineffective," Mulligan explained.
"Following a near drowning incident, in which water has been inhaled, it is vital for parents to monitor their child for at least five hours.
"Everything will appear normal afterwards and then suddenly there's a relapse.
"There isn't a definitive list of signs and symptoms to watch out for. It can be any change in their condition at all: any change in their breathing and any change in their demeanor .
"Parents know their child better than anyone, so if they notice anything different about them following a near drowning incident they should seek medical advice immediately. Take the child to the hospital or dial 999."
"One of the challenges we often have with dry drowning is that the parents won't even acknowledge there has been a near drowning episode," Mulligan addds.
"That's because people have a stereotypical image of what drowning looks like - that people are going to splash and shout - and of course the reality is that this isn't the case.
"But if parents don't realise that the near drowning has happened, then they therefore won't be aware of the need for the ongoing monitoring afterwards.
"This is why it's especially important that parents are vigilant around water. It's not just swimming pools and lakes, drowning episodes can also take place in paddling pools or in the bath.
The Royal Society for the Prevention of Accidents (RoSPA), do not use the term dry drowning or secondary drowning, but David Walker, leisure safety manager at RoSPA, also advises parents who suspect their child may have inhaled water should seek medical advice immediately.
“RoSPA is sad to hear of this incident and our thoughts are with the family," said Mulligan.
"Each year about nine children aged from birth to four years old die of drowning. Drowning is a process where the victim inhales water, which is different from a cough or a splutter.
"Parents who suspect that their child has inhaled water should seek medical help as injury can show itself a few hours later in some cases.
"If a child has lost consciousness after going into water or has difficulty breathing then it is critical that they get emergency help as soon as possible.”
McQueeney's mission to raise awareness is working as her photo has been shared more than 80,000 time on Facebook within a week of being posted.