The 91-year-old was rushed to hospital in NY over the mystery illness.
Stiller's family was with him Wednesday night, the source added.More news: Manchester City ready to help Gabriel Jesus after family return to Brazil
'There are no signs of a stroke. "He's totally fine", a source close to the family told the Daily News.
Jerry's wife -and Ben's mother- Anna Meara, passed away in 2015.
Stiller experienced a resurgence in fame through recurring roles in Seinfeld and The King of Queens (on which his wife had a guest starring role) for all of its nine seasons.More news: Did The Sopranos Kill Tony Soprano in the Series Finale?
The Brooklyn-born amusing man is perhaps best known for playing Frank Costanza on the sitcom Seinfeld, from 1993-1998.
The couple's comedy team, Stiller and Meara, earned success in the 1960s and 1970s, with numerous appearances on variety shows like The Ed Sullivan Show. In The King of Queens, he played another offbeat dad, Arthur Spooner, who was the father of Leah Remini's character Carrie Heffernan.
The pair also shared a daughter, actress Amy Stiller.More news: Donald Trump weighs in on Jeff Bezos' divorce: ‘I wish him luck’