The 32-year-old was maligned for his displays for England in their ill-fated campaign in Brazil, and also struggled at the start of the season for the Toffees as they conceded 10 goals in three games.
However, Jagielka and his teammates are now searching for their third clean sheet in a row in all competitions after rectifying their problems from earlier in the campaign.
"People were quick to point out how bad my loss of form was, but I knew myself it was not as bad as people were making out," Jagielka told reporters.
"I score a couple of goals and I become a better player all of a sudden. That's the way football is.
"You know when you've played well and when you haven't, and I feel for the majority of the season I can look myself in the mirror."
Everton face Burnley in their Premier League clash on Sunday.