The `Not Fair` singer - who is expecting her first child with boyfriend Sam Cooper - received treatment after falling over at London`s Wolseley restaurant on 17.08.10, also injuring her wrist.
Tweeting about her tumble, she posted: "I fell over in the foyer of The Wolsley this morning. Tres embarrassing. Hurty wrist (sic)."
She later tweeted: "Owwwwwcch. My neck hurts. Feel free to Insert sexy time related joke here. Still not funny. My neck hurts a lot (sic)."
The 25-year-old star then received medical treatment on 18.08.10 after her pain got worse.
She tweeted: "At the docs. Its whiplash from my fall yesterday! Oh deary me (sic)."
A source at the restaurant admitted staff were shocked when Lily fell.
One insider said: "Lily really hit the deck. She tried to laugh it off but it must have hurt."
The `Smile` hitmaker - who was left devastated after suffering a miscarriage with then-boyfriend Ed Simons` baby in January 2008 - announced her pregnancy earlier this month after weeks of speculation.