The 78-year-old discovered Katyana Klass lying in a pool of blood after she apparently collapsed in the foyer of her home on Friday (January 27), The Sun reports.
Collins is keeping a bedside vigil at Cedars-Sinai hospital, where 39-year-old Klass is recovering from minor surgery on her cheekbone.
A source said of the incident: "[Katyana] hit her head on the door knob and then the marble floor. Joan spent the night in hospital with her and hasn't left her side. She's very worried and upset."
A spokesperson for Collins told reporters: "Joan's daughter Katyana is recovering quickly and doing well."
Collins claimed last year that a Dynasty revival is in the pipeline and confirmed that she would like to return as her iconic character Alexis Carrington.
She has also been tipped for a role in Downton Abbey.