Hussain complained of chest pain last night following which he was taken to a private hospital here, Bihar BJP President Mangal Pandey told PTI today.
Various medical tests, including ECG, were carried out.
"The problem seems to have occurred due to gas. Hussain has been kept under observation," Pandey said.
BJP president Rajnath Singh enquired about Hussain's health over phone, party sources said.
Party General Secretary J P Nadda, who is in Patna, visited Hussain in the hospital as also BJP Vice-President C P Thakur, Bihar Health Minister Ashwani Choubey and scores of legislators and workers.