Siddall, who had been on court for an hour and a quarter in a finely balanced mixed doubles match alongside compatriot Danny Sapsford, was carried on a stretcher to the nearby medical centre, where she was examined by a doctor and given fluids.Wimbledon officials said she was advised to rest but was not seriously ill.
Meanwhile Arantxa Sanchez Vicario, hoping to bury the ghost that has haunted her at Wimbledon for the past eight years, gave the greatest grass court performance of her career on the Centre Court.
The 23-year-old Spaniard threw caution to the wind to crush the American, Zina Garrison Jackson, 6-1, 6-2 in 64 minutes and advance to the last 16.
This was no ordinary victory. Twelve months ago Garrison Jackson, the runner-up in 1990 to Martina Navratilova and a noted grass court specialist, had beaten Sanchez Vicario after three hard sets.
Many people thought she might repeat the feat against the second seed. In eight previous Wimbledons, the Spaniard has never advanced beyond the quarter-finals despite having won the United States Open and two French Opens.
Normally she is content to stay on the baseline but, knowing these tactics might prove fatal, Sanchez Vicario went to the net at every opportunity and brought off several outstanding volleys. Garrison Jackson was making her 13th and final appearance at Wimbledon.
While Sanchez Vicario was winning on the Centre Court, her compatriot and the reigning champion, Conchita Martinez, was winning just as comfortably, 6-1, 6-1 against the American, Shaun Stafford.
Japanese hopes in the women's singles took a blow when the 15th seed, Naoko Sawamatsu, who has twice reached the fourth round in five previous visits, was beaten in straight sets in the third round by a qualifier, Petra Kamstra. The 210th-ranked Dutch player scored a 6-1, 7-6 win.
Yayuk Basuki, of Indonesia, surged back after a hesitant start to reach the fourth round for the fourth consecutive year by beating France's Nathalie Tauziat - the conqueror of Mary Pierce in the previous round - 6-7, 6- 3, 6-4.
The big-serving Dutch-woman, Brenda Schultz- McCarthy, defeated Slovakia's Radka Zrubakova 6-4, 7-5, but the giant- killing run of Chanda Rubin ended when she lost in straight sets 6-2, 6-4 to the No 9 seed, Anke Huber of Germany.
Martina Navratilova received a standing ovation from the Centre Court crowd when she made her 23rd consecutive Wimbledon appearance yesterday. Navratilova and Jonathan Stark, of the United States, won their mixed doubles against the Americans Matt Lucena and Tami Whitlinger-Jones, 6- 4, 7-6.