Ashton underwent knee surgery during the summer but has come roaring back into try-scoring form after starting the World Cup with two quiet games.
"I do feel I'm back on song again," said Ashton, whose England strike rate is a remarkable 14 tries in 16 Tests.
"It does take a few weeks to get back into it, even though you deny it. It naturally takes a few games to get used to running around and being in position again."
Ashton became the fourth England player to score a World Cup hat-trick - after his fellow wing Mark Cueto had become the third.
Cueto - nicknamed 'Conker Tree' by Ashton and Ben Foden because he's the oldest of England's back three - missed the opening two games of the World Cup with a back injury.
But the Sale wing made an immediate mark on the tournament with three tries in the space of 12 minutes, setting England on their way to a 67-3 rout of the Romanians.
While Ashton had gone five games without a try before his double against Georgia, Cueto's record was one in his previous 25 Tests before Saturday.
"It's good to have the old man back in the team," Ashton said. "I'm glad he scored some tries."
Ashton had a role in two of them before running in his own hat-trick, with two touchdowns in the first-half and the third sealing England's 10-try victory.
"It was definitely nice to reply (to Cueto)," said Ashton. "I was getting a bit scared when he had three and I had none. I wanted a try at some point and thankfully the lads put me in for a few."
Cueto's return alongside Ashton and full-back Foden reunited England's first-choice unit and they carved Romania open time and again.
"The rapport is just a natural thing. Sometimes it happens with players, sometimes it doesn't. You just tend to click," Ashton said.
"We seem to do that. I can't tell you why that is. It's just since we've played together. We kind of know what's going to happen."
Ashton's treble on Saturday took his World Cup tally to five - just three short of the World Cup record held jointly by Bryan Habana (2007) and Jonah Lomu (1999).
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