Williams won the UK Championship in 1999 and 2002
Three-time world champion Mark Williams fell asleep in his chair during a surprise defeat at the UK Championship.
Welshman Williams, 46, lost 6-5 to England’s Anthony Hamilton in the second round in York.
The two-time UK champion missed two tournaments after contracting Covid-19 in October.
“Thirty years as a professional, that’s the first time I’ve ever fell asleep in the chair,” said world number nine Williams.
“It was 3-2 and I was out. My head went down and I woke up and I didn’t have a clue where I was for about five seconds.
“It was a bit embarrassing but I was just shattered.
“I need to be playing in the mornings really, or afternoons. The more the day goes on the more tired I get.
“It’s disappointing but there’s a lot worse people that have had Covid than I’ve had it, so I’m one of the lucky ones really.
“It’s definitely better than what it was a couple of weeks ago so I’ve just got to keep going, but if I play night matches I’m going to really struggle.”
The Scottish Open starts in Llandudno on 6 December.
“It’s only best of seven, so I should be able to stay awake for that one,” joked Williams, who led 4-2 against 56th-ranked Hamilton.
Hamilton won three frames in a row before Williams levelled at 5-5, only for Hamilton to benefit from a massive fluke on a red during a match-winning break of 70 in the deciding frame.
“I’ve had enough flukes in my time, so you’ve got to take one the other way now and again,” said Williams.