“Every night I grab two huge jars and fill them with water and usually get a snack, like watermelon, because I’m always starving and I keep it by the bed so I don’t have to get up and go all the way to the kitchen,” Williams tells PEOPLE.
“I go to bed at like 9 p.m., but wake up at 5 a.m.,” adds the tennis champ, 35, who is expecting her first child this fall. “My brain is different, it’s so weird!”
Want all the latest pregnancy and birth announcements, plus celebrity mom blogs? Click here to get those and more in the PEOPLE Babies newsletter.
RELATED VIDEO: Pregnant Serena Williams Channels Her Inner Na’vi Warrior at Disney’s Animal Kingdom
Williams, who accidentally revealed her pregnancy on Snapchat in April, says she then lies in bed until the sun rises to start her day.
“I just turn on Netflix,” says Williams, a binger of miniseries The Bible. “A lot of people have trouble sleeping during pregnancy, but I’ve been fortunate.”
The mom-to-be says she especially values nighttime rituals — and fondly recalls cuddling with her sisters, including fellow tennis champ Venus Williams, for bedtime stories as a kid.
“Growing up, I would sleep with one of my sisters and they would tell me stories about sisters!” she recalls. “That was my thing. I would say, ‘Tell me a sisters story.’ I was so grateful to them.”
Williams hopes to pass along the sweet tradition to her own baby — with help from her fiancé Alexis Ohanian, of course.
“Alexis is really good at telling stories,” she says. “He loves doing that. One of us will have to tell our baby stories. That is going to be really important to me.”
As Williams’ due date approaches, she is starting to feel some of the pressure, physically. “Through this pregnancy, my weight distribution is different. My stomach is obviously bigger, and my hips are different,” she explains. “I’ve had few problems in general, but some days my back can really hurt.”
FROM PEN: “It Was a Fairytale”: All the Exclusive Details on Tara Lipinski’s Ultra-Chic Southern Wedding
“I lay down on my mattress at the end of the day and it rejuvenates me,” she explains. “As I gear up for such a pivotal year in my life, quality sleep is so important.”
Williams says the idea of juggling motherhood, her intense sport and promoting partnerships is daunting — but she’s up for the challenge.
“It’s a lot, and I know that, but it’s been done before and that keeps me going, knowing a lot of people have done it,” she says. “If they can do it, I know I can do it. I’ll do the best I can.”
The star still remains tight-lipped regarding the sex of her baby, though. “We’re not releasing the gender yet!” she says. “Or any name.”