Later when he returned to his Hawkes Bay home a welcoming party of 15 turned out at the airport for him.
"I kind of knew he would pull through, even though it was pretty hairy for a while there," Mr Cowan said.
"I just think you either know or you don't, but I had faith. He's strong enough to pull through and did. He lost his mum four years ago and I figured she wouldn't let him die."
What caused his collapse remains a mystery, with a report months away. But life has returned to normal for Mr Cowan, who was back at his base in Burnham.
"He's been back for a few weekends and he's back to normal way, and fit. He doesn't say anything - I just ask him how's it going, he says okay and that's it.
"He's tough as nails and he's always been strong, stronger than all the kids when he was growing up - just super-human strength, really."
But he doubted his son would re-apply for SAS selection, saying he had already over-exerted himself.
Details released to the Herald under the Official Information Act show Mr Cowan was among 16 prospective recruits who have been medically withdrawn during selection for the NZSAS in the Auckland region over the past five years.
Seven had to pull out because of heat exhaustion, four over knee injuries, one with a twisted ankle, another because of a shoulder injury and three with unknown causes.
The 10-day selection process - which includes a test to hike 200km in 60 hours with a 45kg pack - is described by the New Zealand Defence Force as a "demanding course designed to identify self-disciplined soldiers and officers who are capable of working effectively as part of a small group under stressful conditions for long periods of time".
Completing the course did not guarantee the candidate could move on to the more demanding training phase.