The 26-year-old was overlooked in favour of Tommy Bowe, Alex Cuthbert, Sean Maitland and George North last Tuesday, with his omission widely predicted across all four Home Nations despite the fact that he had been seen as a certain tourist not so long ago.
Ashton equalled the try-scoring record for a single RBS 6 Nations Championship with six touchdowns in 2011 and then finished the World Cup as the joint leading try scorer alongside France's Vincent Clerc but his Test career has stagnated somewhat since.
The former rugby league star says the lure of the Lions played a role in his downturn in form, even though he knows it should really have brought out the best in him.
"The Lions has been in the back of my mind all year and it's done my head in a little bit," Ashton told the Daily Mirror.
"You know it's coming and, because it's something you so much want to be a part of, it kind of distracts you.
"It shouldn't, it should motivate you to play better. But sometimes that makes you over-keen and want to do too much."
Ashton bounced back from the disappointment of failing to win a squad spot with Britain and Ireland's elite by scoring for club side Saracens on Saturday as they beat Bath to secure top spot in the Aviva Premiership.