"I don't know what I did last night. I drank too many different types of drinks, I guess. But after the ball we went to a bar and there was about 30 or 40 friends there.
"We had a great time. I got to bed at five and I woke up and I didn't feel good."
Federer tentatively plans to resume at the Cincinnati Masters on August 13 before chasing grand slam No.20 in New York a fortnight later.
A six-month lay-off to physically recover from a knee injury and mentally recharge after two decades of tour grind, then another break during this year's claycourt season have proven spectacularly successful for the peerless Swiss.
But he knows it will be a challenge going forward to remain as competitive, with less and less match practice as his body and eye get older.
He also accepts it's a balancing act and, while he can see himself playing for years to come, Federer is realistic too.
It's why he told fans on tennis's famous centre court he "hoped" to return next year to defend his crown.
"Honestly, ever since I had the year I had last year, I do think probably like a year ahead of time with my schedule, fitness schedule, tournaments I would like to play. So I totally see myself playing here this time next year," he said.
"But because it's far away, because of what happened last year, I just like to take the opportunity to thank the people in the very moment, and make them understand, yes, I hope that I'm back. There's never a guarantee, especially not at 35, 36."
The Times of London has dubbed Federer the "eighth wonder of the world" but even he never dreamed of being so wildly successful.
"Winning eight is not something you can ever aim for, in my opinion," Federer said.
"If you do, I don't know, you must have so much talent and parents and the coaches that push you from the age of three on, who think you're like a project.
"I was not that kid. I was just really a normal guy growing up in Basel, hoping to make a career on the tennis tour."
