Doctors recommended Declan get a CT scan, a procedure that requires a person to sit completely still.
Being jittery by nature, Declan had to be sedated.
9 News reports the doctor grabbed the wrong syringe, injecting Declan with a much stronger sedative, causing 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 since made a full recovery and an investigation is underway to figure out how the almost deadly mistake happened.
Dr Peter Thomas, Nepean Hospital’s director of medical services, said, '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.
'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.'