Mark Williams apologised after falling asleep during a match for the first time in his career as he was beaten in the second round of the UK Championship.
Two-time champion Williams, 46, suffered a surprise 6-5 defeat to Anthony Hamilton.
Williams contracted Covid-19 in October and said that was the reason why he drifted off halfway through the match against Hamilton.
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"Thirty years as a professional, that's the first time I've ever fell asleep in the chair," said world No 9 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."
Williams also apologised on Twitter for the incident, saying: “It has nothing to do with Anthony, I just don’t feel well from Covid.”
Williams is likely to compete next at the Scottish Open, which starts on December 6.
"It's only best of seven, so I should be able to stay awake for that one," he joked.
Williams made a strong start against Hamilton as breaks of 65 and 66 helped him open up a 3-0 lead.
Hamilton won the next two frames to close the gap, but Williams responded with a break of 71 to edge closer to victory. Having drifted off, Williams then saw the match slip away as Hamilton made three half-century breaks in a row to move 5-4 ahead.
Williams roused himself to level at 5-5, only for Hamilton to benefit from a fluke on a red during a match-winning break of 70 in the final frame.
"I've had enough flukes in my time, so you've got to take one the other way now and again," said Williams.

'Thoroughly deserved to win the match' - Selby hails Vafaei after shock

The tournament continues on Monday with the third round at York Barbican.
World No 1 Mark Selby also crashed out on Sunday as he went down 6-2 to Iran’s Hossein Vafaei.
“I didn’t play good enough,” said Selby. “Hossein was definitely the better player and deserved to win. He started off great and is a great front-runner, and if you let him get away he can blow anyone away.
"I didn’t really get a chance the first two frames. Hossein played great, settled really quickly.
“I probably should have won the third frame, missed an easy black off the spot and had half a chance in the next frame, so could have easily been 2-2 at the interval. But after the interval he kicked off great again and thoroughly deserved to win the match.”
Vafaei came into the UK Championship on the back of his 5-0 win over Ronnie O’Sullivan at last month’s German Masters qualifiers.
“Beating the top players is a big achievement for anyone,” he said. “They are our legends so I have to respect them, if they lose or win their names are always there, we don’t forget who they are. Mark Selby is one of the great ambassadors for us and such a nice champion.”
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You can stream the 2021 UK Championship live and on demand on discovery+ and watch all the action live via Eurosport and at eurosport.co.uk
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