It started during his single tour of Afghanistan's most volatile war zones as the driver of a refuelling truck loaded with 10,000 litres of diesel. His nickname was "Fireball" for the most obvious related hazards.
Near misses included rocket attacks, the horror of a suicide bombing that killed several children, firefights, roadside bombs and long weeks outside the relative safe zone of the Kandahar Airfield.
Sleep became elusive and fraught with nightmares. MacWhirter, 37, chronicles them along with the tedium punctuated by terror of a grunt's existence in his new memoir "A Soldier's Tale: A Newfoundland Soldier in Afghanistan."
"It was over a year before I realized something was different," he said of his return to Edmonton. "What threw me over the edge was, even today, I get angry for no reason.
"There are times when I'm really angry at the world and I sit down and try to figure out why I'm angry. And I can't."
Almost seven years since he returned home, MacWhirter sees a psychiatrist regularly and figures he probably will for life. He got clearance from the military to publish his recollections based on a journal he kept while overseas. He wanted to convey what troops and their families go through on volunteer missions that take a steep toll both during and after deployment.
"Every soldier that I have talked to from my tour has something, whether it's nightmares (or) they're still on medication," he said. Many of his buddies quit the military.
"Others got kicked out because they turned to drugs or alcohol. Every soldier from my tour changed a little."
MacWhirter's girlfriend at the time, Vanessa, is now his wife. Military spouses who juggle household duties while trying to keep thoughts of the worst at bay are often baffled by the haunted soldiers who return home, she said.
"What he went through I could never imagine," she said during a family interview at their home in Goulds on the outskirts of St. John's, N.L.
"You never quite get the understanding of the feelings that he gets when it comes to the post-traumatic stress disorder or the nightmares that he goes through.
"I think a lot of people try to hide it and they think they don't need it, but support can really do a family wonders."
Jamie MacWhirter has high praise for military efforts such as the Operational Stress Injury Social Support program in which fellow soldiers help each other to cope and heal. But his book documents the frustration of rotating psychiatric staff and reliance on prescription drugs.
"When I get a new head doctor I have to start all over again," he writes. "When I leave an appointment, I find myself very tired or in a bad mood because I just spent the last hour reliving things I would just as soon forget.
"Why can't we talk about what could cool me down when I get angry? No, they would rather talk about what makes me angry then give me some pills."
MacWhirter said it's crucial that soldiers find something that truly gives them peace. For him, it was being posted in 2010 back to his home province, Newfoundland. He was born in Corner Brook on the island's west coast and now works as a station dispatcher in St. John's. He is no longer on medication, he said.
"It was like it took a rucksack off my back," he said of being back on the Rock. "My father has a cabin in Cormack and that is my safe zone."
Being able to share with his two young boys Avery, 12, and Cody, five, the joys of fishing, swimming and camp fires has helped more than counselling ever did, MacWhirter said.
A report funded by the Canadian Forces and written by military staff, published last month in the Canadian Medical Association Journal, concludes almost 14 per cent of members who served in Afghanistan suffer from related mental health disorders.
It found that eight per cent of personnel who deployed between 2001 and 2008 were found to have post-traumatic stress disorder. Another 5.5 per cent of that group struggle with depression.
The research included 30,500 troops and used the medical records of a random sample of about 2,000 of those.
MacWhirter hopes his book will help other troops and their families.
"The war continues when that soldier comes home."