The dad-of-one, from Cardiff, suffered liver and kidney failure once the infection from the bite had spread around his body.
Alan's family believe he was bitten by a tropical spider as he brought in imported goods where he worked at a Tesco distribution centre at Magor in South Wales.
His sister Lynda Conniff, 56, said she knew something was wrong when his fingers began to swell up "like sausages".
She said: "He came home from work complaining of groin pains - his job involves lifting so we thought it was a hernia but it was followed by a rash.
"The rash got worse until it was bright red and then his fingers swelled up until they looked like fat sausages."
Within hours Alan was rushed to the University Hospital of Wales in Cardiff and was moved to the intensive care unit.
He fell into a coma and doctors told his family he may die.
Lynda said: "He lost a month of his life - we were told to expect the worst."
After a whole month, Alan finally came round.
Tests are still being carried out by doctors as they try to find the cause of his illness.
Supermarket customers in South Wales have recently complained that they had been bitten by non-poisonous spiders nested in imported bananas.
But Tesco, who are supporting Alan, have denied claims that he would have been handling fresh food at Magor.
A spokeswoman for the company confirmed that they will not release a full statement until medical test results are known.