Mercedes' Lewis Hamilton admits he has not been at 100 percent since clinching the world championship in Mexico last month.
The Briton sealed his fourth title with two races to go, but a crash in qualifying in Brazil and his inability to beat team mate Valtteri Bottas in Abu Dhabi perhaps reflected a loss of motivation as the season came to a close.
"I have tried my hardest to stay on it but I wouldn't say it was 100 percent of what it was while in the season," Hamilton said.
"You want to enjoy it. I do still try and turn up and do the job but it's not so easy.
"It's clear that something happens once you've won the championship. All I can say is that in the week after I won the championship, I partied a lot.
"That's what you do. I didn't do that before the other races.
"The energy has not been the same, even if I have approached the races the same. But I'm not worried about that. Next year it will go back to what it was in the second half of the season."
Mercedes boss Toto Wolff isn't sure where the relative under-performance may have come from, but insists he isn't the least bit worried about the future.
"He is somebody who is very diligent in progressing," Wolff explained.
"He had an accident in qualifying that happened after he has won the championship. And where that comes from I don't know.
"These guys are pushing the cars to the limit. He didn't put a foot wrong all season. I'd rather it happened after the championship than before.
"Here he looked very good until qualifying and then Valtteri put it all together and I think you just have to acknowledge this was Valtteri's weekend."