Former deputy first minister Martin McGuinness has declined to disclose the nature of his illness. He said on Monday his health is a personal and private matter.
While there has been speculation that Mr McGuinness is suffering from a heart condition, he refused to reveal what he is being treated for.
There was considerable shock at Stormont on Monday at the deterioration in his health.
At Stormont Castle, he said that his illness was not a factor in his decision to resign as deputy first minister. When asked whether he would be standing in the expected forthcoming Assembly elections, he said he would decide that matter closer to the time.
The first word of his illness came last month after the 66-year-old Sinn Féin politician did not travel with First Minister Arlene Foster on a trade mission to China. At the time, Sinn Féin said Mr McGuinness had to withdraw from "a planned visit to China this week on medical advice and to enable doctors to conduct a medical assessment".
