Some nights, David Klemmer closes his eyes and pleads with himself.

"Please don't wake up. Please don't wake up. You're OK."

Three to four times a week he will wake up not knowing where he is, sometimes screaming into the darkness.

Klemmer suffers from night terrors. At least he thinks that's what it is.

"I don't know if I'm a weirdo," Klemmer says of the nightmares he has had since he was eight years old. "I probably should go see someone about it, shouldn't I?"

"I've been doing that since I was a kid.

"One of the first nights I stayed at my missus' [family home] I went through it. Her family thought someone had a machete and was cutting me up, that's how loud I was screaming."

His wife Chloe, who was his girlfriend at the time, slept through the whole thing.

Why Klemmer had to leave the Bulldogs for Knights

"There was no sleeping in the same bed for the first couple of years, so she was in a different room," Klemmer says with his trademark booming laugh.

But her parents, John and Julie, were horrified to walk in to see their daughter's boyfriend standing on the bed copping repeated hits to the head from the ceiling fan while yelling "get off me, who are you?".

Chloe says: "They were like 'what the hell has our daughter brought home? Who is in our house?'."

Listening to Klemmer explain it, you don't know whether to laugh, end the interview or do a Google search for ways to help.

Until now, he hasn't really divulged some of the reasons for wanting to depart the Bulldogs.

But on the eve of his first trial at the Newcastle Knights, he skims the surface of what he has been battling.

"I've got stuff going on in my head," he says.

"I've always doubted myself. As a person, as a player - I've always doubted myself. You've got this expectation to be a player, a role model. I've always doubted that.

"Just going to the shops I've always got anxiety about people looking at me. It's something I had to deal with. You know how I am - I'm just a big kid. I don't know. It's just how I am. I like to keep to myself."

What you see from Klemmer on a football field - the crazy eyes and the white line fever - is far from what you get off the field.

But the assumption of his character that people form from his on-field behaviour is often hard to ignore.

"When I go out, that's the perception people get," Klemmer said.

"They think you're that all the time. Obviously on the footy field, if I come across you, that's how it will be. But off the field people expect you to be this big angry person 24-7.

"I struggle to deal with that. People are always trying to stir you up to get you angry. There's a lot at risk if I slip up and do something like that. I'll lose a lot of things."

When you sit back and listen to what Klemmer has been through and experienced, it's hard to imagine how he managed to get himself in the position he now finds himself in both as a professional footballer and a father of three boys that he adores.

Klemmer; It feels like I've started first grade again

As a teenager, Klemmer rebelled. He hung out with the wrong crowd and any chance of forging a career out of rugby league looked unlikely.

"I thought I was invincible," he says.

"I did stupid things. Things I'm embarrassed to talk about. I'm just lucky I had football. Because the people around me in that time of my life didn't. I could have been like them. I could have wasted my life just doing stupid things in Fairfield.

"But when I made the Harold Matts side at the Bulldogs I made a choice to change my life. It was around the time I met my missus. So if I wanted more out of life I had to change. I've seen things happen to people at a young age. That could've been me. But I had football."

Chloe's parents, like many who see Klemmer for the first time, wondered if he was indeed as frightening as his giant stature suggested.

"The first time my mum met him we went to the movies and we were waiting for him to come," Chloe recalled.

"I told Mum 'be aware he's very tall'. She said 'is this him walking over now? How old is he? Does he go to school?' The first time Dad met him we were playing netball out the front of my place and dad pulled up from work.

"Dave was so shy and nervous. Dad just walked inside and said to mum 'how does Chloe know this man? Who is he? Are you sure he goes to school with her?' He looks like a big, tough, angry man but when you get to know him you realise he's just a big softy."

Nothing has made him softer than his three sons - Cooper, 5, Jaxon, 3, and David, 1.

It's why Klemmer was an emotional wreck last year when he broke the news to his eldest son that they would be packing up and moving on from the Bulldogs.

"I was pretty nervous," he said.

"He was watching telly and I said 'mate, can I have a yarn to you'. I said 'I've got something to tell you'. I said 'mate we're going to have to move homes and change footy teams as well'. He gave me this blank look and had a tear in his eye.

"It was pretty hard looking at him and telling him. He sort of said no. I felt pretty bad saying you have to. It was pretty hard seeing him upset because he was so settled.

"He was pretty upset. He didn't want to change teams. I finally got him over the line. But it was pretty tough. That was harder than talking to the media and all those cameras. But I know this is the best thing for him as well. Coming up here, he obviously doesn't see it now but when he gets older it'll definitely be better for him as well.

David Klemmer's 2018 season highlights

"My wife said there's a good chance we won't ever be going back. This could be us up here now. It's just the start of things. Hopefully, I can see my kids grow up here and really become the boys they want to be and enjoy their upbringing. They are why I do this.

"They don't understand now but in 10 or 15 years time when they look back to me playing footy - they were part of it. They've got photos with [Cameron] Smithy, Billy Slater, Johnathan Thurston, Gal [Paul Gallen] … I want those moments for them to capture all this so they can remember it all and make them proud."

Klemmer never wanted to leave the Bulldogs. He grew up wanting nothing more than to play for the team he loved.

"I remember my neighbours as a kid, Mohammed and Ali," Klemmer said.

"As soon as we got home from school, we'd be on the road playing footy until about 7 or 8 o'clock every night. We were actually all Doggies supporters. Pretending that we were all playing for the Bulldogs."

But through his own battles, and that of those around him, he began to realise the nature of modern-day sport.

"I always thought of myself as a one-club man," Klemmer said.

"Probably after the break after the season some stuff hit me pretty hard. Just where I was at in my life. I had a good think about it … I went away on holiday and had a good think about where I was at in my life and my footy and where I want to go.

"I don't want to stay the player I am. I don't want to stay the person I am. I just didn't want to think what I was doing was good enough. I was doing the exact same thing. I want to go up and beyond.

"I just thought this was a great opportunity to do it. And that's rugby league now. The clubs can tap a player on the shoulder or move a player along at any time.

"James Graham was the captain of our club and got moved on. It left a huge hole in the joint. Grubby [Josh Reynolds] as well - as characters outside of football they played a big part in the culture of the club. Mick Ennis as well. He was there as captain of the club. Aaron Woods was there and got moved on halfway through the year.

"That's the stuff that happens in rugby league. It's a business now. I was only a kid - 22 or 23 when all this stuff was happening. At that age I was always thinking I wanted to stick solid and be loyal and finish my time here. But the things that were happening in my life, I thought my time at the Dogs was done."

Rugby league has somewhat been a safe haven for Klemmer. It's where he feels at peace, as bizarre as that might sound about such a brutal sport.

"Just going on the field there's nothing to worry about," he said.

"There's nothing that can harm me or do anything. It's nice and relaxed. It's the place I love to be. I wouldn't want to do anything else. I love playing footy. I still have the same love for it that I did when I was six years old. I'm just very lucky to be in the position I am in."

Tattoed over Klemmer's chest is "one life, one chance".

It's one chance to amount to something. One chance to be a somebody.

"I'm scared to think what I would be if I didn't meet Chloe and make it in footy," Klemmer says.

"I'd be 150 kilograms with a big mullet. I'd be a nobody."