Serena Williams finally realized what happened days later, when she was allowed to get out of bed.

Williams said she was barely aware of how sick she was as she tried to play through a viral infection that caused her to lose equilibrium during a women’s doubles match with sister Venus at Wimbledon. It was only later, when she was able to clear her head, that she realized the seriousness of her situation.

“It was interesting and I was scared after,” Williams said. “I didn’t realize how I felt until later. In the moment I didn’t realize how sick I was. It’s weird but that’s the fight in me. I never know when to say when.”

She would have continued had not Venus insisted she get off the court.

“She kept saying, ‘walk off the court, I’m the older sister and I say you have to leave.”’ Williams said. “I’m feeling really good right now and I’m happy to be here.”

Williams said she will undergo a series of tests at the end of the season. “I was really ill,” she said. “I got to thinking about a lot of things and because of family history, I’ll get the tests done and we’ll go from there.”

Williams meets the Czech Republic’s Karolina Pliskova on Wednesday in the second round of the Bank of West Classic in Stanford, Calif. – Associated Press