Justice Simon France reimposed the 20-year sentence, meaning Lundy faces a minimum of eight further years behind bars.
That prospect would have had a major psychological impact, University of Canterbury criminologist Greg Newbold said.
"It will be completely devastating.
"When you're doing a long time in jail you get used to it, you get settled into it and you start to forget about the outside."
During Lundy's period out of prison he would have experienced two psychological effects, Professor Newbold said.
"One, he remembers all the pleasures of freedom and he's living in a different world and will begin to forget the prison world.
"And secondly, I think he really thought he had a good chance of being acquitted and his mind wasn't set on the idea of going back - in his mind he would have been planning an acquittal and carrying on with his life."
Being sent back to prison will "knock him for six psychologically", Prof Newbold said.
Lundy would also have suffered a physical reaction to hearing the verdicts.
Prof Newbold was himself convicted of drug dealing charges in 1975.
"When I was convicted...I felt like all my blood drain out of my feet, I just felt the most awful feeling of dread go right through my veins.
"I'd say that's what Lundy went through yesterday."
Prison officials will need to keep a close eye on Lundy while he settles back into prison life in case he attempts to harm himself, Prof Newbold said.
"It takes months really to settle back in."
