The American superstar pulled out of the evening's team event, as her American team mates surrendered gold and their title to Russian gymnasts.
"There is more to life than just gymnastics," Biles said, saying a focus on her well-being was her goal.
"It is very unfortunate that it has to happen at this stage because I definitely wanted these Olympics to go a little bit better. But again, take it one day at the time. We'll see how the rest goes."
Such late-night drama was a fitting end to a day which had begun under the threat of a tropical storm, and then featured the loss of the face of the Games, tennis star Naomi Osaka. loading
Osaka had brought the issue of mental health into sharp focus earlier this year when she pulled out of the French Open Grand Slam tournament. This had been her first tournament since saying she has been suffering depression for several years.
"I definitely feel like there was a lot of pressure, this time around," Osaka said. "I think it's maybe because I haven't played in an Olympics before and for the first one to be here was a bit much.
"So... I didn't really know how to cope with that pressure."
America's gymnastics silver team medal means Biles can no longer win six golds here which, added to her haul of four from Rio, would have made her the most decorated female Olympian of all time.
She had arrived in Tokyo as the superstar of these Games, and expectation was at fever pitch.
It appears it may have proved all too much.
"It just sucks when you are fighting with your own head," Biles said. "You want to do it for yourself but you're just too worried about what everybody else is going to say, think, the internet.
"So I just had to stay off of it for the past couple of days. It's just like when everybody tweeted you and you feel that weight of the world. I felt it, and at the end of the day, if I had pushed through that... okay, this is for me. It is for me, but I feel like I have do to it for other people first."
Biles could still, in theory, win five and match the current record, but it seems increasingly unlikely.
Russian great Larisa Latynina won nine gymnastic Olympic golds in the 1950s and '60s. Only Michael Phelps, with his 23 swimming golds, has won more.
Osaka, who lit the Olympic cauldron on Friday to open the Games after a one-year postponement, looked out of sorts and never settled into a rhythm as she lost 6-1 6-4 in the third round to Czech Marketa Vondrousova.
Her departure left Japan without its best known global sporting figure in the Olympics, one whose multi-ethnic background contrasts with the image of an insular and male-dominated country that emerged in the run-up to the event.
The Games are taking place under a state of emergency and without spectators, an unprecedented event in the history of the modern Olympics.
Tokyo reported 2,848 infections on Tuesday, in line with warnings from health experts that the summer would bring a rebound in COVID-19 cases due to increased mobility and the spread of variants.
FIRST SURFING MEDALS
While Osaka was out, and Biles diminished, other competitors enjoyed better days.
Brazil's Italo Ferreira and American Carissa Moore overcame challenging conditions in brilliant style to win historic first Olympic surfing gold medals.
In the women's triathlon, Flora Duffy achieved instant national hero status when she won a first gold medal for Bermuda, the smallest of the 206 nations and territories in the Olympic movement to win a Summer Games title.
In the pool, Russian Evgeny Rylov broke a U.S. stranglehold on the men's 100m backstroke, while Tom Dean powered to gold in the men's 200m freestyle, heading a British one-two with Duncan Scott taking silver.
Japan won their second successive gold in softball, beating the U.S. 2-0 and by the close of the day Japan led the medals table with 10 golds, one ahead of the U.S. and China, both on nine. Reporting by William Mallard, Rozanna Latiff, Ju-min Park, Farah Master, Philip O'Connor, Sam Nussey, Linda Sieg and Antoni Slodkowski; Writing by Ossian Shine; Editing by Toby Davis