The horrific attack happened on Monkey Island near to the popular holiday island of Phuket in southern Thailand.
"I thought I was heading for safety under this rock in the shade, only to cool down," Mrs Darwell, from Peterborough, said.
"I laid the towel down and there were no monkeys in sight.
"The next thing I noticed, this monkey walked up next to me and I thought, oh dear, and I began to stand up to move away.
"Then, the monkey took my wrist and pounced on my right arm, sinking his teeth in and hung off it.
"He wouldn't let go; he was locked on. I was absolutely petrified."
Thai fishermen ran to the rescue after spotting more monkeys joining the assault and began prying them off.
Mrs Darwell said she had agreed to go on the Siam Sea Canoe tour with a friend to confront her fear of monkeys.
Her phobia had been triggered by her father bringing up a chimpanzee which she described as "positively evil".
She said: "I thought, this is it, I'm going to die, I'm going to be savaged by these monkeys - then I went into shock."
Mrs Darwell added: "I wouldn't have got off that bloody boat if the tour guide would have said at all that there was any danger, any risk, even the slightest risk."
Tour leader Mr Yongyut Buasod said: "We can't control the monkeys if they decide to bite someone, that's why we always warn the tourists.
Full story here.