However, the British women's No.1 is no soft touch and despite serving "at about 50% at first" and having treatment for dizziness, Watson still managed to make it through to the second round, defeating Alexandra Cadantu, of Romania 2-6, 6-3, 6-2.
The world No.50 said she planned to see a doctor before her second-round match with Ksenia Pervak, of Kazakhstan, tomorrow but the one thing that can be guaranteed about Watson is that she will give absolutely everything she has.
"Last time I played her was in the Australian Open juniors at the quarter-finals," Watson said. "I lost. She won [the title] that year. But I've seen her around. She's a lefty, a tough player, she makes a lot of balls."
On the surface, Watson is happy-go-lucky, always quick with a smile and genuinely nice but there is also a real steel about the 20-year-old that often gets overlooked and she was more annoyed with her performance than pleased with the recovery.
"I'm not really proud of it," she said. "At the beginning I definitely wasn't there. I wasn't playing well. I didn't have much energy. I don't know what it was.
"When I started cramping, I had to start hitting the ball [harder] because I couldn't move. I'm kind of thankful that I did cramp today, otherwise I don't know how the match would have ended up."
Trailing by a set and 3-2 and making an unusually high number of mistakes, Watson called the doctor, who took her temperature.
At the same time, Cadantu needed two injury time-outs and the extra time to recover was crucial for Watson as she roared back to victory.
"I was worried because I wasn't playing well, at all," a candid Watson admitted. "I thought it was a great opportunity, not being drawn against a top-five player in the world. I really wanted to take advantage. I had a great finish to last year and this is the first grand slam event of the year, so I was really looking forward to it, very motivated.
"She actually had two time-outs, so during that time I just ate two bananas, some gels, drank loads. I think having that little sit down, I got a little recharged and motivated."
Last October, Watson became the first British woman to win a WTA Tour title since 1988 when she won in Japan and the confidence she derived from that has helped her reassess her aims for 2013, with a place in the top 30 her next goal. "I feel a lot more confident and I believe in myself," she added. "Like this match, I felt I should have won and if I didn't I would have been extremely disappointed.
"I'm using it to push myself more in my training, make sure I'm working hard every day and not having a slack day."
Laura Robson, just three places behind her in the rankings, was due to play the American Melanie Oudin in the early hours of this morning.