The 33-year-old actress - who gave birth to son Bingham last July - said that Hawn told her to "imagine [her] va-jay-jay as a magnolia flower blossoming".
"I called my mum to tell her I'm in the hospital and in labour," Hudson told chat show host Ellen DeGeneres.
"She was like, 'OK, well, how much time do I have? Because I was going to take a swim'... I have not eaten in like 10 hours [and then] she shows up with a pizza and Doritos [and says to me], 'I'm starving'."
Hudson added: "She [brought] a magnolia flower... she did visualisations with me. She told me, 'Imagine your va-jay-jay as a magnolia flower blossoming'."
The How to Lose a Guy in 10 Days actress also revealed that her fiancé - Muse singer Matt Bellamy - tried to invade her privacy during the 18-hour birth as well.
"I was like, 'Stay back'," she said. "I put up tarps.
"I was like, 'Don't go anywhere near the area', and I [saw] him start to creep. I [was] like, 'No, no, get back!'"
The 'Madness' singer recently admitted that witnessing his son's birth "freaked him out" as nobody had warned him "how horrible it would be".
Bellamy and Hudson got engaged in April last year, but the actress has said that they do not plan to get married any time soon.