He fell to the ground in "fear and haste" before shouting to his colleagues that the man had a gun.
"I got myself together and chased him out of the station, I don't know why I chased him but I did. The two other guys there they didn't hesitate either, they were straight out after me.
"As far as I know no one has spoken to them about the situation either."
Mizzi, 44, later pleaded guilty to threatening to cause grievous bodily harm to three police officers, including Mr Berkett, and possession of an imitation firearm.
In the Napier District Court yesterday he was sentenced to two years' jail.
Mr Berkett returned to full duties a couple of days after the incident but said it quickly became apparent he was not coping with the trauma.
"Emotionally, I was a wreck and fearful of what each day would bring. Family life was a struggle as my wife did not want me returning to work. Our young daughter developed deep fears of me not returning home from work," he wrote in a letter to the Police Association News.
Mr Berkett said he went on two weeks stress leave to recover, yet was contacted only by his immediate supervisor, Sergeant Gary McFadyen, and members of his own section.
After returning to work he found it difficult to work and took two and a half months' unpaid leave.
He struggled to return to the job.
"It's pretty scary when you know something like that could happen. It's not worth it when you've got a young family."
He eventually resigned and said he was not contacted by anyone from Human Resources.
"No one seemed interested in why I was resigning and I wasn't offered a leave of absence. I was not asked to complete an exit interview, which is actually police policy. I felt really let down."
In response to the letter, former Eastern District Commander Superintendent Sam Hoyle also wrote to Police News.
He said while he acknow ledged the incident clearly had an impact it was "unbalanced" of Mr Berkett to claim management didn't have contact with him.
"I accept the trauma policy was not implemented on Christmas Day, the day of the event, by his NCO as it should have been."
Yet he said over the following weeks Mr Berkett was contacted by various senior staff. He stated the former constable's letter was not "entirely reflective of the effort put in by welfare staff and a number of the area and district managers to assist him".
Mr Berkett said he was visited by one senior sergeant but did not want to play "tit for tat" with Mr Hoyle.
"My big gripe is to make sure it doesn't happen to anyone else.
"I just don't want others to go through it, especially with all the bad stuff that happens to police."
Police Association vice president Luke Shadbolt said Mr Berkett's situation was unique in that systems put in place to deal with trauma have significantly improved over the past few years.
"Brendon's situation is a bit unique in that the systems to a certain extent have let him down in the initial stages."
He said it appeared Mr Berkett had "slipped through the cracks".
