The presenters informed ITV viewers that guest Samuel Carvalho had been "flat out" shortly after discussing his black-outs, which have been aided by a pet pooch.
After his moving chat about how his dog had helped him with the debilitating condition, all seemed well until the programme returned from an ad break.
Phillip, 54, informed fans: "Welcome back. I'm a little bit shocked at the moment, because we were just chatting to Samuel, who said as he got up: 'Oh thank goodness, I managed to get through the interview without passing out.'"
The star continued: "He's fine. He's got a paramedic with him now… But, as soon as he left the studio floor, it was right outside the studio door – absolutely flat out."
This Morning: Samuel Carvalho fainted moments after finishing interview today
This Morning: Phillip Schofield later revealed what had happened off screen
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BBC presenter Victoria Fritz went into labour live on air, but managed to continue to read out the headlines as fellow newsreaders rushed to help
As soon as he left the studio floor, outside the door – absolutely flat out.
Phillip added: "Hopefully, at some stage, someone will find out what that is and that dog will help to prevent that from happening."
Samuel had tweeted prior to his appearance: "Be sure to tune into ITV’s This Morning tomorrow to watch me give a live interview. Here’s hoping I don’t collapse during it!"
Many took to Twitter to comment on his condition, with one user writing: "#ThisMorning What a lovely young man with his gorgeous dog. I hope he gets his medical issues resolved #mansbestfriend."
This Morning: Samuel Carvalho tweeted to say he was worried about fainting
This Morning: Samuel Carvalho has suffered substantial injuries after fainting
Another went on: "I suffer from the exact same thing, but my dog just looks at me and walks off if I black out #ThisMorning."
"So lovely to know that their are other people who have faints & episodes like I do. It's horrible condition to have! #ThisMorning #ITV," a third posted.
This Morning airs weekdays at 10.30am on ITV.