Jonathan Thomas talks easily and fluidly about the severe head trauma he endured as a rugby player. The former Wales international, who won 67 caps and was part of two Grand Slam-winning sides, was forced to retire last month. A combative and inspirational player who burst to prominence with a brilliant performance against New Zealand in the 2003 World Cup, Thomas was diagnosed with epilepsy a year ago. He also suffered mild brain damage as a consequence of blows to the head.

It’s a difficult subject but Thomas is an insightful witness. He only pauses when fearing he might be misunderstood. “The last thing I want is to sound as if I am being critical or trying to persuade anyone not to allow their children to play rugby,” he says on a quiet morning at his home near Tewkesbury. Thomas and his wife, Laura, have made coffee and laid out a plate of shortbread which the retired backrow forward can now enjoy. But the biscuits are soon forgotten as Thomas tells his story.

Last season, with medication controlling the seizures that marked the onset of his epilepsy, Thomas helped Worcester gain promotion to the Premiership. He played 19 games, including two decisive play-off matches against Bristol, and his commitment to rugby remains undimmed. “Not for one minute do I think the rules should be changed or the game toned down,” Thomas says. “I just think players need to be educated about the dangers of playing with head trauma. They take a bang to the head and think: ‘I’ll play on because I’ve two days off after the game.’ That’s doing serious damage.

“I’ve been guilty of staying on the pitch at all costs. It’s the gladiatorial mindset and it’s difficult to shake. I’ve always believed in playing hard and you have a laugh with your team-mates if someone in the squad is a bit soft. You give them a kick up the backside and say: ‘Come on, let’s go to war . . .’”

Amid the blazing intensity of a World Cup that has enthralled Thomas, it’s easy to talk of epic battles and savage defeats – but it is sobering to absorb Thomas’s words about head trauma. “You need that mindset as a pro to play on despite niggles and injuries,” he says. “But if I’d known back then what I know now about head trauma I would have handled many situations very differently. I hope players and coaches can learn these lessons and change the way they react to head injury. Even when you’re a kid, you get knocked over and the coach immediately says: ‘Come on, jump back up, get stuck in.’

“I don’t think players of my generation can change that mentality but it’s important for the coach of the under-nines to get the kid off rather than saying: ‘It’s the cup final, play on.’ Same with the academies – that’s the generation we need to target.”

Thomas talks openly and he debunks many misconceptions. "When I say 'a bang' I don't mean the concussions George North went through or what happened to Liam Williams against England. That's a no-brainer where he gets knocked out and taken off. The George North incident at Northampton looked horrific [when, in March, the wing suffered his third serious concussion]. But when that happens the brain shuts down and you have a period of recovery.

“The consultant who worked on my epilepsy said being knocked out is not as bad as playing on with trauma. It’s the bangs you get head-on-head or the back of your head hits the floor and you play on even though you know you’re not right. The medical staff wouldn’t be able to see it but your brain rattles inside your skull – and that can happen in mini-rugby. That’s when the serious trauma occurs because you shake your head and play on.”

Thomas picks out a possible moment when his epilepsy emerged – and it was not a bone-rattling hit which knocked him cold. “Let’s rewind to the Gloucester game in December 2013,” he says. “I took an innocuous clash to the head with my team-mate and didn’t really flinch. But for the next 35 minutes my mind went completely blank. I couldn’t remember any lineout calls or even my role in the team. I was getting deja vu-type flashbacks. At half-time I felt sick and came off. I’ve had bad knocks and usually you’re fine a few days later but for three weeks I kept failing my return-to-play protocols. Eventually I came back and played the remainder of that season without obvious problems.”

Worcester were relegated in Thomas’s first season after he had enjoyed a successful career with his home region in Wales. At Ospreys, he helped them to four Pro12 league titles and the Anglo-Welsh Cup. It explains why he was Dean Ryan’s first signing as the director of rugby at Worcester. Thomas duly helped his side win promotion back to the Premiership but that campaign was blighted by epilepsy which rose up even before the season began.

“I did almost the whole pre-season until I tore my calf,” Thomas remembers. “The seizures then started when I was doing flat-out fitness. This was not running work because of my calf. It was all rowing, bike fitness. I didn’t know I was suffering mild seizures. It’s since been explained that they’re petit mal – a mild seizure. A grand mal is when people with epilepsy have proper fits and became unconscious. I never had one of those, fortunately. With petit mal you’re getting mini-seizures. It’s like dreaming while you’re conscious.

“One day I was doing weights and I started getting flashbacks. They last about 30 seconds. If one happened to me now you probably wouldn’t notice – but I would. Someone looking at me would think I seem a bit dazed but you snap out of it. Initially I put that down to intense training where you feel lightheaded. Around that time – and this lasted six weeks when I didn’t tell anyone – I was also getting huge memory loss.”

We can hear his wife chatting away to their baby daughter, Maya, in the kitchen, while their son, Kobi, is at school. The impact on his family ran in tandem with the problems he encountered at Worcester. “When my wife asked me what I’d done in the day I’d be at a loss,” he admits. “Normally it takes a few seconds to recall the day but it was taking me a minute to think: ‘What the hell did we do today?’ I’ve always prided myself on a strong memory but I’d be mid-conversation with my wife or as part of the Warriors’ leadership group and forget what I was about to say next. I’d start speaking and midway through my first point I’d completely forget the other points. It got embarrassing and I became reluctant to speak.

“All these things sound worrying but at the time they were so subtle. After six weeks I flagged it up to the doctor. She said: ‘Gosh, that sounds like mild epilepsy.’ I was naive and thought she was overreacting but they sent me for these scans and epilepsy was confirmed. Physically I was raring to go but you think: ‘How the hell is someone going to let me play with that?’

Thomas says Worcester "sought the best advice in the country", which led him to Dr Oliver Cockerell, a consultant neurologist based in Harley Street. "He was great. He said we need to get your seizures under control with medication. If we can do that, and we monitor you, I can't see any reason for you to stop playing. As soon as I had a sniff of that I thought: 'Great.'"

Thomas was assured that, as long as his seizures were controlled, he faced no higher risk than any other player when taking a hit to the head. “At first the medication seemed great. All the seizures stopped but my capacity to train hard and recover was not the same. I could get up for a one-off game but it was taking so long to recover.”

His consultant tweaked his medication and he was even given a sleep hormone, but Thomas’s last season was shattering. During games his level of play remained consistent but, afterwards, he felt exhausted. The 32-year-old was even more drained after training.

“I was sacrificing everything to play well for 80 minutes on a Saturday. Off the back of that everything fell down. I was getting personality changes. I’m usually very laidback away from rugby but I was irritable and suffering with short-term memory loss. I would give my all on the Saturday – and they were almost wheeling me out for the next game.

“I went from being a dad who after training would be out in the garden with the kids, but then I’d come back from training and go into the spare room – unable to be myself in the home. In the play-offs, because I was so fatigued, we decided Laura and the kids would move back to her parents for a few weeks. I was completely resting and that was the only way I got through.”

Thomas never made an official announcement to his team-mates. “But you tell one or two and it spreads through the squad. Obviously the management and medical team knew. I just didn’t want all that sympathy with everyone asking: ‘How are you?’ I had this huge desire to help the club back into the Premiership. I didn’t want people worrying about me.”

Dean Ryan, his coach, is the only other rugby professional Thomas knows who has admitted his own epilepsy was a direct consequence of too many blows to his head. "Dean went through the same towards the end of his playing career with Newcastle. He had far worse seizures for a longer period and so he was very knowledgeable and a huge help."

They shared in the elation of Worcester’s promotion but during the summer Thomas realised he and his family were under terrible strain. His consultant advised him to retire. “He said if you stop now you could lead a completely normal life if you look after yourself. The consultant said there had been an element of brain damage and my memory recollection might not come back completely. He decided it was time.”

Thomas looks up. “I don’t want to dramatise anything. I almost count my blessings. You see people who have two or three grand mal a day. I’m very lucky.”

He is wise enough to gather himself before committing to a future path. “All I know is I definitely want to stay in the game. I think I’d have a passion for coaching but I want to take a few months out to look after my health.”

Thomas looks fit and he is an engaging and thoughtful man. He is also passionate about Wales and the World Cup – and full of affectionate anecdotes about the special people he has met in rugby. “I have great memories,” he says. “And, at 15, if I’d been offered what I went on to achieve in rugby I’d have jumped at it. But as a sportsman you’re always greedy. It’s that old mindset. You’re never content. You always want to play on but it’s different now. I can accept everything. I have no regrets.”

(Guardian service)