The Charlie's Angels star was reaching above her wardrobe to retrieve an object when she lost her balance and tumbled to the ground, reports Britain's The Sun newspaper.
Her boyfriend Justin Timberlake ran to her aide and rushed her to hospital after finding her bleeding on their bedroom floor.
The Sun reports Diaz was treated for a back strain and received 19 stitches to her head.
A friend says, "Justin was frantic with worry. At first the paramedics thought she had broken her back. Although she was bruised, fortunately it was just badly strained.
"Justin insisted on staying by her side in the ambulance."
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