His parents Jessica Newsome and Blake Campbell thought they’d be safe and take their boy to Nepean Hospital, in Sydney’s southwest, to get doctors to double-check the growing egg on his head.

Doctors recommended Declan get a quick CT scan — a medical procedure that requires a person to lie completely still.

Being a jittery baby, he had to be sedated — but it was when the doctor gave Declan his needle that they knew something went seriously wrong.

The doctor had grabbed the wrong syringe, injecting Declan with 12mg of intravenous Suxamethonium instead of 12mg of Ketamine, according to his discharge papers seen by 9 News.

Suxamethonium is much stronger than Ketamine and causes short-term paralysis.

Ms Newsome witnessed the entire terrifying ordeal, seeing her baby boy’s lips turn blue and his body go limp.

“His body just froze,” Ms Newsome told 9 News. “He was just limp. He was just nothing. He went straight pale.”

The terrified mum then turned to the doctor and told him “something’s wrong”.

“He just picked the kid up and ran,” Ms Newsome said.

Declan has made a full recovery and an investigation is underway to figure out how the almost deadly mistake won’t happen again.

The two syringes with the very different drugs were in the same tray, with the doctor accidentally grabbing the wrong syringe.

Ms Newsome said her and her partner still have nightmares about the situation, remembering the 90 seconds their little boy stopped breathing and having to watch him get carried away on a metal tray.

The mum also said she knew something was wrong when a staff member working in the CT room burst into tears.

Mr Campbell rushed to the hospital after a call from his worried partner detailing what had happened.

“Something should have been so simple,” Mr Campbell said.

“Just go for a quick CT scan just to make sure he had no problems and it happened to turn out to be he nearly died.”

Nepean Hospital has been contacted for comment.

Previously, Nepean Hospital’s director of medical services Dr Peter Thomas told 9 News processes were in place to make sure it’ll never happy again.

“While the baby was in the emergency department, the treating doctor apologised for the mistake and provided full disclosure, explaining to the parents what had happened and a social worker provided support to the parents,” Mr Thomas said.

“The Director of the Emergency Department also met with the parents that day and apologised.

“The baby recovered and the Hospital will implement the recommendations of the review to prevent the mistake from happening again.”