Lewis Hamilton revealed he had been "battling demons" during a difficult year after claiming his sixth Formula One world title on Sunday.

The Mercedes driver finished second at the United States Grand Prix to win his third championship on the bounce, with team-mate Valtteri Bottas topping the podium.

However, the Briton dismissed suggestions his latest triumph had come easily, hinting at battles on and off the track during a year in which friend and mentor Niki Lauda passed away.

"No way has it been the easiest," he said. "It's been the hardest year for us and the team. We lost Niki this year, a crucial and pivotal member of this team. The emotional rollercoaster that we've been on with losing him, and I didn't have Bono [race engineer Peter Bonnington] here for a race.

"Outside of the car, just trying to remain focused throughout the year, that is the toughest – and I guess only other athletes at the top of their game can relate to it.

"Week in, week out – you can't drop the ball like I did [in qualifying], for example, and being able to bounce back from the lower days.

"This car has not been easy for us. We started the season going to Melbourne thinking we were going to be behind. At the mid-point of the season we were behind, it's been a real challenge this second half of the season.

"I think it's the toughest second half of the season that we've had as a team, fighting against Ferrari and Red Bull. We welcome that.

"But I don't know: every journey's different. Every year you go through a different roller coaster of emotions to get to where you're going and I wrote something in my post this morning that each and every one of us is struggling with something in life, whatever it may be – small or big.

"I tried to show people that from the outside things always look great but it's not always the case, and I'm also struggling with lots of different things.

"I'm battling demons and trying to make sure that I'm constantly growing as a person."