But while NBC canceled two episodes of "Tonight" when Jay Leno fell ill in May, there was no word from the network on plans for next week's shows following O'Brien's mishap.
O'Brien was examined Friday at a hospital. The network declined comment on his condition or whether he had been released.
O'Brien issued a statement through NBC that indicated he was treating the incident lightly.
"Last thing I remember I was enjoying the play with Mrs. Lincoln, and the next thing I knew I was in bed being served cookies and juice," O'Brien said in the statement.
A "Tonight" rerun with guest Jeremy Piven aired Friday. According to NBC's Web site, the scheduled show was to include Teri Hatcher and Seth McFarlane ("Family Guy," "The Cleveland Show").
The 46-year-old comedian took over the "Tonight" host's job from Leno in June.
Leno's absence came toward the end of his 17 years with the show, when a high fever and unspecified illness caused him to check himself into a hospital for a day.
NBC canceled two episodes of "Tonight" when that occurred in May. Leno's new daily prime-time comedy show debuted this month.
NBC's decision to remove the top-rated Leno from "Tonight" and replace him with O'Brien, hoping to draw a younger audience, put pressure on the new host's shoulders.
The network's creation of a daily prime-time series for Leno, displacing five hours of scripted shows, was another bold move.
NBC is owned by General Electric Co.
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