"I kept saying the Lord's Prayer. And I kept thinking about my parents. And I kept seeing lots of green lights and blue lights. I didn't see the Beatific Vision or Peter standing at a gate saying: 'What the hell do you want? It's not your time. Go back. Clear off.' There was nothing like that."
Five days after he was admitted to critical care, doctors gave Stack a trial drug. The day after, medics were standing at his bedside when they noticed that he raised his left eyelid as they were discussing him.
As he lay stricken in bed, he didn't know that a pandemic had overrun the country and the population was now confined to home.
"At first I didn't realize the seriousness of what was going on, mainly because there were no televisions. There was no press. Being so ill, one didn't want to read anything. I had no stamina. My energy levels were almost nil," he said.
"And the next thing was, you've got these people dressed in white spacesuits, saying: 'We're the COVID team.' I said: 'What the hell's that? Is it the Olympics or something?'"
It took some time for hospital staff to establish that Stack was a Catholic priest. But once they did, a Catholic chaplain visited and gave him the Eucharist and the Sacrament of the Sick. He also received consoling visits from a Baptist chaplain.
A turning point came thanks to an unexpected act of kindness.
"I was slumped in a chair in critical care," he said, noting with a chuckle that the phrase rhymed. "I was kind of like a zombie. One of the doctors came up to me. She sat in front of me and said: 'Is there anything I can do for you?'"
"I couldn't speak because I had a tracheostomy in my neck with the oxygen going in. So I just shrugged my shoulders. She said: 'Would you like a shave, Michael?' I nodded my head. So she spent about an hour giving me a shave. I had a beard and my hair was terrible."
"Then she opened the curtain, took the bowl of water away, and met her other colleagues. She said: 'I get an extra 10 bonus points: I just shaved a Catholic priest.'"
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Stack was on a ventilator for 21 days and in critical care for 36 days. When he was moved to a new ward at the end of April, he began the arduous process of starting to walk again.
"Three jolly physio people turned up dressed in their masks and hoods. They said: 'Hello, Michael, we're going to get you to walk.' I said: 'How?'"
"With the first push and shove, they got me to put my feet on the ground. They lifted me forward and moved me two steps. That was the beginning of the process of learning to walk again."
Stack was, of course, used to hospitals, but as a chaplain rather than a patient. He estimates that he has ministered to around 5,000 people who have died on wards. As well as serving at some of the U.K.'s busiest hospitals, he was also national chaplain to the Association of Catholic Nurses in England and Wales.
A few years ago, he published a book about the Church's healing ministry. "Lord, When Did We See You Sick?" tells 12 stories of grace amid illness drawn from Stack's ministry. In a foreword, Cardinal Nichols described it as "a moving testimony to the healing power of our prayerful companionship with the sick and dying."
Stack noted that the title is from a passage in St. Matthew's Gospel where Jesus says that we will be judged according to how we treated "these least brothers of mine."