Cheryl Cole is being treated by doctors for a tropical disease called malaria.
The X Factor judge recently announced she was taking some time off work to rest after reports she had fainted at the weekend.
It's thought Cheryl could have caught the disease during a recent trip to Tanzania, in Africa.
Malaria is spread by mosquitoes and can be deadly. But if it's spotted early enough it's easily treated with the right medicine, so Cheryl should be OK.
X Factor judge Simon Cowell told the singer: "Don't rush back. Health is a priority and get some rest to recover properly."
Ricky finds out more about malaria
Malaria is one of the biggest diseases in the world - it's thought one child dies from it every 30 seconds. It's most common in tropical places, such as Africa, southern Asia and South America.
The illness can feel a bit like the flu at first - symptoms include a headache, aching muscles and feeling really tired.
That's followed by a high fever and then chills, every few days. The illness can last up to three weeks.
Every year, around 2,000 people from the UK become infected with malaria when abroad, but if treated early, people can make a full recovery.