Romain Grosjean has admitted the 2012 season took its toll.
With a 2013 seat secured, Frenchman Grosjean went on holiday.
“I think it was good to have a break, it did me good,” he told RMC Sport.
“I was much more tired than I thought. It’s about realising just how much fatigue has accumulated, and knowing really what a full season of formula one is about, and that it is not so simple,” added Grosjean.