The volcanic eruption and tsunami hit the island nation on Saturday, sweeping Atata local Lisala Folau out to sea.
Mr Folau told the BBC that he held on to a floating log during his 27-hour ordeal at sea, before finally reaching the shore again.
Tonga has confirmed three deaths though the extent of damage is still unknown.
Mr Folau, 57, told the BBC's Newsday programme he was scared when he saw the wave approach, but "I had my faith in God he would save me".
"When I was in the water I remember going under eight times. My legs are disabled and don't function as well," he explained. "The sea kept twirling me and taking me underwater."
He said he then managed to grab hold of a floating log.
"I could hear my son calling from land and I didn't want to answer because I didn't want him to swim out to find me... I just twirled while holding onto the log," Mr Folau said.
"What came into [my] mind is at sea there is life and death. Until you reach the shore, then you know if you're alive or dead."
Meanwhile, aid has now started trickling in with more governments deploying ships and flights to the country.
Communications have been crippled, with the only undersea cable that connected Tonga to the outside world ruptured in two places.
A New Zealand ship which arrived at Tongatapu, the main island, on Friday was the first foreign major aid ship to land. It was carrying 250,000 litres of water and has a desalination plant on board which can produce up to 70,000 litres of clean water every day.
The UN says clean water supplies are the top priority for the Pacific nation.
However, authorities also revealed on Friday that water testing on the main island showed it is safe for drinking.
"Some communities on Tongatapu have however lost access to drinking water. Drinking water is being delivered to the outer islands," said the New Zealand government.
It added that despite emerging reports of missing people, the death toll remained at three so far: two Tongan nationals and a British national.
Australia has deployed its largest ship, the HMAS Adelaide, which set off for Tonga on Friday and is expected to arrive mid-next week. The ship can carry helicopters which can then be deployed to take supplies to Tonga's smaller outer islands.
The UK announced on Friday that it was also redeploying its vessel, HMS Spey to Tonga, and had already sent aid supplies with the Australian ship.
"The UK will work closely with Australia and New Zealand to assist the recovery effort in Tonga and stands ready to support our long-standing Commonwealth partner," said UK Defence Minister Ben Wallace.