Senator Ted Kennedy remained in hospital in Washington overnight after suffering a seizure during yesterday's inaugural lunch for President Obama.
Testing suggested the seizure was 'brought on by simple fatigue,' said Dr Edward Aulisi, the Washington Hospital Centre chairman of neurosurgery.
'Senator Kennedy is awake, talking with family and friends, and feeling well,' Dr Aulisi said in a statement.
He is expected to be discharged later today.
The 76-year-old Democrat has been receiving treatment for a brain tumour since it was diagnosed in May last year.
He missed much of the rest of the year in Congress, but returned to the Senate after the Democrat Obama's election in November, determined to help the new president pass sweeping legislation to expand health care.
Ted Kennedy endorsed Barack Obama's presidential bid last January, giving a crucial boost to a relative Washington newcomer from one of its most seasoned hands.
A Massachusetts senator since 1962, he is known for his full-throated support of liberal policies, health-care expertise and thick shock of silver hair.
Mr Obama, who shortly before had been sworn in as president, said after the seizure that his prayers were with Mr Kennedy and his family.
President Obama did not know what was happening when Mr Kennedy became ill at a table during the traditional formal lunch in the Capitol's Statuary Hall.
'When he found out he rushed out,' said Sen Daniel Inouye, a Hawaii Democrat.
Barack Obama quickly returned to the lunch as Ted Kennedy was taken away for treatment.
The 200 lunch attendees, including former presidents, Cabinet nominees and other government officials, later said a prayer for Mr Kennedy.
