It comes on slowly; creeping in the background, inch by inch, until it can consume you – and it doesn't discriminate. Whether you're a big-time entertainer, a blue-collar worker or a sporting superstar, depression can sink its claws into you.
It's not something you wake up feeling physically ill with one morning, and you don't exhibit any clear signs. It affects everyone in different ways. For UFC middleweight champion Robert Whittaker, depression had him considering hanging up his gloves.
The Auckland-born mixed martial artist opened up on his battles with mental illness to Grange TV this week, with depression getting a hold of him while he was recovering from injury after a fight against Yoel Romero in 2018.
"It starts slowly, like you just don't feel like going out or training," Whittaker explained. "Your mate will call you and instead of answering you'll look at your phone and be like 'I can't be bothered' and put it down or you'll get text messages and you just can't be bothered replying.
"That's how it starts. Then you try to get out of sessions because 1. there's no drive taking you there to do it and 2. the feeling of going to the session and getting absolutely hammered and feeling unfulfilled, it's double-backing on itself … then you're double depressed and you don't want to go to the next session.
"I just retreat within myself. I just feel bad, I just feel terrible. I feel unmotivated, and it gets worse and worse and worse."
Whittaker was suffering the effects of the illness in the lead up to UFC 234 in Melbourne in February this year, where he was scheduled to defend his title against American Kelvin Gastelum but was forced to withdraw due to emergency surgery. Speaking to Submission Radio, Whittaker said as he got back into training when he had healed from the injuries sustained against Romero he felt like he had fallen behind and couldn't perform at the level he thought he should be able to.
"It was a hard time for me to motivate myself to keep going, to motivate myself to feel good. I was very apathetic and didn't want to do anything.
"I just reached a point where I felt it was either do or die for me – I had to just start hitting the sessions, I had to get through it, I had to bite down on the mouth guard and just plod along or not. The alternative would have been to hang up the gloves and call it in. I wasn't ready to do that.
"It wasn't like I wanted to pick up a new hobby or start a new job; I didn't want to do anything. I just wanted to have naps; I didn't want to leave the house.
"It wasn't specifically a sport related thing, it was just everything. I was just tired of it all."
Depression is one of the world's most common illnesses, affecting more than 300 million people worldwide according to the World Health Organisation (WHO).
It can cause the affected person to suffer greatly and function poorly at work, at school and in the family. At its worst, depression can lead to suicide. Close to 800,000 people die due to suicide every year.
Although there are known effective treatments for depression, including medication and psychological treatment, fewer than half of those affected in the world receive such treatments. In some countries, fewer than 10 per cent of those affected receive treatment of the illness, WHO reports.
Whittaker credits the support team around him for helping through the tough period and pulling him out of the darkness, and said he's in a great place now ahead of his title unification bout against interim champion Israel Adesanya in Melbourne in October.
In December, when the dust has settled from the bout against Adesanya, Whittaker will embark on a speaking tour of Australia in New Zealand, where he will open up about mental health, his life in general and fighting for every opportunity he was presented.
"I'm a very guarded person. I find it very hard to let people in as well as speak about anything that is even a little bit uncomfortable for me. But that's what I want to get out of this speaking tour – to let people in."
If you are worried about your or someone else's mental health, the best place to get help is your GP or local mental health provider. However, if you or someone else is in danger or endangering others, call 111.
If you need to talk to someone, the following free helplines operate 24/7:
DEPRESSION HELPLINE: 0800 111 757 LIFELINE: 0800 543 354 NEED TO TALK? Call or text 1737 SAMARITANS: 0800 726 666 YOUTHLINE: 0800 376 633 or text 234
There are lots of places to get support. For others, click here