Up 21-3 when Kubiak went down leaving the field at the break, the Texans unraveled in the second half, falling 27-24 to the Indianapolis Colts for their sixth straight loss after opening the season 2-0 with Super Bowl hopes.
"We were all very worried," quarterback Case Keenum said. "When we went back out they told us he was ... stable. We were all upset about that but trying to stay focused at the same time."
Kubiak hunched over and dropped to his knees at the 24 yard line and was immediately surrounded by medical personnel. He was lifted off the field on a stretcher and taken by gurney to the ambulance.
The Texans didn't say what was wrong with Kubiak, but did say he didn't have a heart attack and he was in stable condition. The team said the 52-year-old coach was conscious and was with his family as he was taken to the hospital.
"He had an episode, he was light-headed and dizzy," Texans general manager Rick Smith told NBC after the game. "He was evaluated by a number of specialists ... he is awake and coherent.
"He went to a knee, and they laid him on the ground. He is stable; for precautionary reasons we wanted to get him to the hospital. We have to assess ... obviously, there's a lot of info. Hopefully, Gary will be back with us tomorrow."
Andrew Luck rallied the AFC-South-leading Colts (6-2), throwing three second-half touchdown passes to T.Y. Hilton. Luck has 10 game-winning drives in the fourth quarter or overtime, the most in a quarterback's first two seasons since 1970.
"I don't think we freaked out or got out of our system," Luck said. "I think we settled down a bit and played ball."
Keenum threw for 350 yards and three touchdowns in his second career start, but had trouble moving the offense after halftime.
Houston had a chance to tie it, but Randy Bullock's 55-yard field goal attempt as time expired sailed wide left.
Defensive coordinator Wade Phillips took over the Texans after Kubiak left.
"There was a lot of unknown," Phillips said. "It was a shock to everyone."
The Colts took their first lead of the game when Hilton grabbed a 9-yard touchdown reception and Coby Fleener caught the 2-point conversion to make it 27-24 with 4 minutes left.
Bullock missed a field goal early in the fourth quarter and the Colts cut it to 24-19 when Luck found Hilton on a 58-yard touchdown pass two plays later.
Houston built the halftime on Keenum's three touchdown passes to Andre Johnson. Johnson had 190 yards receiving at halftime, but just 39 yards after that.
The Colts scored nine points in the third quarter, highlighted by a 10-yard TD pass from Luck to Hilton on a third-and-10 to make it 24-12.
Adam Vinatieri kicked field goals of 30 and 35 yards in the second and third quarters for the Colts.
Keenum hit Johnson, who had gotten in front of Vontae Davis, for a 62-yard touchdown pass on the third play of the game to give Houston a 7-0 lead. It was the first touchdown reception of the year for Johnson.
J.J. Watt blocked a field-goal attempt on the Colts' first possession and rookie D.J. Swearinger returned it 37 yards. But Houston couldn't convert and Indianapolis got the ball back when Ben Tate was stuffed on fourth-and-1 from the Indianapolis 16.
Johnson added a 41-yard touchdown reception with 4:21 left in the first quarter. It marked the first time since 2010 that Johnson caught two TD passes in a game.
The Colts had a first down at the Houston 7 late in the first quarter after a 46-yard pass interference call on Kareem Jackson. But the Texans sacked Luck on second down and an incompletion on third down forced Indianapolis to settle for a 30-yard field goal that made it 14-3.
Johnson's third touchdown came on a 5-yard reception just before halftime.
Luck was sacked three times in the second quarter - twice on the Colts' first drive of the period __ as Indianapolis struggled early.
Notes: The Colts were playing their first game since losing star receiver Reggie Wayne for the season. Wayne tore his right ACL in an Oct. 20 win over Denver and had season-ending surgery. ... Texans running back Arian Foster, who missed practice earlier in the week with a hamstring injury, left late in the quarter with a back injury and didn't return. ... Colts receiver Darrius Heyward-Bey was evaluated for a concussion, but coach Chuck Pagano said after the game that he did not have a concussion.