According to People, the singer became ill when cold medicine she took reacted negatively with other unspecified medication she had previously taken, a source told the mag. Amy has been admitted to the London Clinic since Sunday.
Though the 26-year-old singer has endured a series of health issues in the past, her father, Mitch Winehouse, said in October that Amy has been "healthy for a year."
He also gave Amy's fans an update on her recent breast enhancements, on Britain's "This Morning" program last month.
When describing how his daughter is doing, Mitch said, "Fantastic, fantastic. Her boobs are great as well."
Realizing he perhaps spoke out of turn, Mitch added, "I shouldn't have said that should I? She looks absolutely fantastic."
People's source agreed with Mitch telling the mag that Amy is pleased with her recent plastic surgery and has made her feel "really good about herself … She's been saying how she wants to get back in the gym."