The football coach said that you inevitably start "to think about all kinds of sinister things" when your loved one is seriously ill, with COVID-19 worsening pre-existing issues with Sandra's vocal cords.
Redknapp told the Sunday Mirror that Sandra contracted the virus in January, following a New Year's Eve visit to a restaurant, and spent the next six months fighting the symptoms.
"Sandra has suffered. Her voice had packed up and she was struggling for breath. Even swallowing food became difficult. She could choke on food easily if we weren’t careful," said Redknapp.
He added: "The symptoms weren’t good, if I’m truthful. You start to think about all kinds of sinister things. It’s been a real worry."
Sandra said that the virus "attacked previous surgery" she had on her neck and so it left her with a selection of serious problems.
As a result, she had to undergo multiple surgeries in order to bring about a recovery, with some of them leaving her unable to talk for several days.
She added: "I was struggling with it for six or seven months. Even now if I’m talking a lot my voice starts to get a bit sore. But, fingers crossed, I’m on the mend."
The Redknapps met as teenagers and have been married since 1968. They will know reveal all about their 50-year love story in new book When Harry Met Sandra.
"We’ve been very lucky. The ups have outweighed any downs, for sure," said Redknapp.
He added: "We don’t argue. We have disagreements, like everybody, but I can’t say we have any real fallouts. We never have. We just get on great together."
When Harry Met Sandra will be available in bookshops from 29 September.
Watch: Harry Redknapp makes TV history with quiz show mishap