He was airlifted to hospital.
He says he had left his gun lying next to him when a big wave knocked it against a reef.
"With that motion, the spear went off and shot through my head. I was able to stand and call for help while walking backwards," he explained.
"It was also to keep myself knowing that I was alive. Some fishermen came out to my rescue and then the paramedics."
Hallowell, who has been spear fishing for 10 years, says he is recovering well.
He was discharged from the hospital yesterday, after a successful surgery.
The path the spear took missed some vital areas," he said.
Hallowell says doctors have cleared him to begin snorkeling again in about two weeks.
He says he has been spear fishing for about 10 years.
"I'm just one of those guys who loves being in the water."
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