Williams - who is a three-time world champion - fell to a 6-5 defeat to Englishman Hamilton in York on Sunday and it seems his performance was a tiring one as he was spotted sleeping whilst his opponent was at the table.
Following his in-play power nap the 46-year-old revealed he 'had no clue where he was' when waking up, in arguably one of his most embarrassing moment of his illustrious snooker career.
He said: "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."
Williams had contracted Covid in October, and suffered fairly severe symptoms - recently revealing he was 'in bed for five or six days shivering'.
And the Welshman believes the knock on effect of his illness was to blame for his tiredness in the match.
He added: "I need to be playing in the mornings really, or afternoons. The more the day goes on the more tired I get.
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"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.”
Williams went on to add that whilst his symptoms have improved in recent weeks, any more evening games he is forced to play may be a 'struggle' for him.
"It's definitely better th
an what it was a couple of weeks ago," continued the three-time world champion.
“So I've just got to keep going, but if I play night matches I'm going to really struggle."
After his defeat, the 46-year-old took to Twitter to apologise for his 'unprofessionalism' following his nap, admitting it was 'embarrassing' but nothing to do with his opponent’s game.
He tweeted: "I would like to apologise to anyone watching tonight, in 30 years as a pro I have never ever fell a asleep in my chair before, it's was nothing to do with Anthony btw.
"I just don't feel well from covid. Bit embarrassing and not professional."