The ex-Eastenders star had been trekking near Khun Si Falls when he fell and became trapped between rocks.
He was left stranded for three days before being rescued.
Speaking to the The Sun, Paul said: “I am lucky to be alive.
“I had a phone with me but I fell from such a height into the water it was irretrievable.
“It took such a long time to find me. It’s an understatement to say it wasn’t a great situation. It wasn’t that I was lost.
“The problem was I couldn’t move to get out of there.
“I’ve got a broken leg and I’m missing a kneecap. It needs complete reconstruction.”
The Sun reported how Nicholls had hired a motorbike under his real name of Gerrard Paul Greenhalgh and went off exploring the jungle when the accident happened.
The source said: “He was out there by himself because he was between filming.
Paul shot to fame in the 1990’s after starring as Joe Wicks in the popular British soap Eastenders.
He also appeared in a Bridget Jones movie and has starred in Law and Order: UK and Holby City.