“Although it is heartbreaking for me to have to step away, my focus has to be on my personal health in the short term and concentrating on getting a better understanding of the issues, and the right support to move forward.
“My absolute priority right now is myself and my family.”
Thomas played 67 times for Wales and won Six Nations Grand Slams in 2005 and 2008, as well as playing in two World Cups.
He started his playing career at Swansea before joining Ospreys, later moving to Worcester in May 2013 for two seasons before his epilepsy diagnosis.
“Lots of people will know about my history and why I had to retire from playing,” Thomas added.
“I’ve had lots of honest conversations with [Swansea RFC managing director] Keith Colclough in the last few weeks and he has provided unbelievable support. I can’t thank him enough. He has been incredible.”
Thomas began his coaching career with Bristol, where he was in charge of defence and the forwards, before returning to Worcester, initially as forwards coach before taking on the head coach job.
He left the Warriors in January 2022 and joined Championship side Ealing Trailfinders as a forwards consultant in September that year.
He then joined the Wales set-up as contact area coach, leaving that role in December 2023.
Thomas first signed for Swansea as a player when he was 16 years old and his appointment as head coach of a team he said had “always been close to my heart” felt significant.
“I was incredibly excited to take on this challenge in the summer and am really proud of the progress the team has made,” Thomas added.
“We’ve got a good squad who want to improve and challenge, and all the signs are that we are heading in the right direction.
“I was loving the job and that makes it even harder for me to make this decision, but it is the right thing for me personally.”
Thomas leaves with Swansea fifth in the 10-team Super Rygbi Cymru and the club said it will provide an update on the coaching situation “in due course”.
