Heather Watson admitted the effects of glandular fever at its worst left her “absolutely exhausted” after a 20-minute walk.
But the Briton has announced her intention to compete at the French Open after returning to training recently.
Watson revealed last month she was suffering from the illness, which left her sapped of energy and forced her to recuperate at home in Guernsey.
“You have to be patient. If you come back too soon you run the risk of a relapse,” she told the Daily Telegraph.
“So I just needed to rest and make sure. At the worst point, I would go for a 20-minute walk in the day and be absolutely exhausted. I was sleeping for 14 hours a day, I was just so tired.
“I hardly did anything, I was in the house every day. In a way it was nice to have that break, but now it’s even nicer to be back training again.”
The last match Watson played was in Miami in March, when she lost from a strong position in the first round and then said she felt burnt out and needed a break from the game.
She quickly backtracked, saying it was disappointment talking, and attempting to play through the symptoms of glandular fever was undoubtedly taking its toll.
Watson, who turned 21 last Sunday, only returned to training two weeks ago but will go into the tournament at Roland Garros, which gets under way this Sunday, in optimistic mood.
“Confident-ish. Two weeks ago, I started training. The first week was literally an hour a day to see how I felt and how my body reacted to it. Obviously I reacted well and we have just kept stepping it up and up,” she added.
“In the past I haven’t always needed too many matches to get ready. When I played the US Open juniors I hadn’t played a tournament. I rocked up and I won it. I did think about playing Strasbourg last week, but after a week of training I wasn’t going to be ready.”