Defense attorneys asked for and received a delay of Thursday's hearing after arguing their client's situation made it impossible for him to appear in court, The Denver Post said.
While attorneys did not provide details about their client's condition, the Post cited unnamed sources as saying Holmes rammed his head into a wall at the Arapahoe County jail.
Arapahoe County District Court Judge William Sylvester postponed Thursday's hearing to Dec. 10 and 13.
Holmes, who has attended all other hearings in his case, is accused of opening fire during a midnight showing of "The Dark Knight Rises" July 20 in a movie theater, killing 12 people and injuring at least 58. He faces 166 counts of murder, attempted murder and other charges related to the shooting.
Citing concerns that revealing Holmes' "medical or psychiatric information" would waive his right to keep other personal information from being divulged in court, public defender Tamara Brady declined to discuss his ailment during Wednesday's hearing, the Post said.
"In the middle of the day yesterday [Tuesday], we received information for the situation [that] involved a trip to the hospital," she said.
Prosecutor Rich Orman objected, saying what information the defense provided wasn't enough to determine whether the delay was justified.
"It's so black-letter law we actually learned it in law school," Orman argued. "That's not the way the law works."