Brighton winger Anthony Knockaert has revealed he battled depression following the breakdown of his marriage and the death of his father.
The Frenchman says suffering with the illness made it "mentally impossible" for him to perform in the Premier League last season.
He went through a divorce last summer, less than a year after his dad Patrick died in November 2016.
Separating from his wife also reduced the amount of time he was able to spend with his young son.
"I was going through depression last year, it was really tough and mentally impossible for me to go and perform on the pitch," said Knockaert.
"I went through a divorce last year during the pre-season, so it was really tough to take, especially after (the death of) my dad."
"When I lost my dad, the most important thing for me was my wife and my baby.
"They were the people that I needed and six months later, I realised that they weren't here any more and just went through a depression. I didn't see it coming.
"There were times I wasn't even focused on the pitch and thinking about the game.
"When you're going through things like that, you realise that you can't always do what the manager asks of you."
Knockaert was named Brighton's player of the year as they won promotion to the Premier League in May 2017.
The 26-year-old admits subsequent difficulties in his private life caused him to be moody and argumentative, as well as affecting his performances on the pitch as Albion adjusted to life in the top flight.
He eventually confided in club captain Bruno in December and, after speaking to Seagulls manager Chris Hughton, was given counselling sessions.
"It can just catch you out," added Knockaert. "I was one of those - even two, three or four years ago - to say when people talked to me about depression 'what is this?'.
"You don't really take it seriously until it happens to you, then you realise what life is about because you are going through the worst period of your life.
"The worst is you never think it will go away, that you will be like this for the rest of your life.
"I was making myself scared, thinking I was starting to become crazy.
"I was always in a bad mood, arguing with people. That wasn't my fault, I was going through a bad period and just didn't control anything else."
Knockaert, who is expected to make his 100th start for Albion when they host Tottenham on Saturday, has already created three goals in five appearances this season.
He contributed just three goals and one assist in 33 league games last season and was hurt by criticism of his ability.
"That was the worst for me, to see some comments saying I'm not at my level, I'm a Championship player," he said.
"It was really hard to take, because I knew there was a reason.
"I wanted to leave a message to the fans, to almost apologise for what I was doing on the pitch last year, but it wasn't my fault.
"When you have help from the club like I did again last year it's just something special.
"That's why I am here today, happy and ready to go again and do even more for this club."