Roberts, 52, was vacationing in Maine when he fell on a dock after having a seizure, Supreme Court spokeswoman Kathy Arberg told the Associated Press. Arberg said the chief justice had only minor scrapes when he was admitted to Penobscot Bay Medical Center in Rockport.
After keeping Roberts overnight for observation, doctors said they found no trace of a tumor, stroke, or any conclusive explanation for the seizure. Arberg said doctors believe there is "no cause for concern."
White House spokesperson Tony Snow said President Bush talked to Roberts on the telephone and said Roberts "sounded like he was in great spirits."
Roberts had a similar seizure in 1993. Snow said the Bush administration was aware of Roberts' medical history before he was appointed.
By definition, a person who suffers at least two unexplainable seizures is said to have epilepsy. Doctors, however, caution the term suggests frequent episodes, and people with epilepsy often have just a few seizures throughout their lifetime.
Because this is Roberts' second seizure, the likelihood that he will one day suffer another is about 60 percent, the AP reported. Anti-seizure medications exist and could be available to Roberts with a prescription from a doctor.
Paul Garcia, a neurology professor at the University of California, San Francisco, told Bloomberg News that Roberts' seizure was nothing out of the ordinary. He explained approximately 10 percent of Americans will suffer a seizure at least once in their life, about half of which are unexplained.
"When any seizure is self-limited and stops on its own after a few seconds to minutes, and we don't know of any lasting repercussions, then we don't have any reason to think there are repercussions," Garcia said.
Arberg said Roberts plans to continue his vacation at a summer home in Maine.