Other causes of nausea include side effects from medications, pain, pregnancy and morning sickness, seasickness, viral infection, alcohol toxicity, and disease of the brain, esophagus, stomach, gallbladder, liver, pancreas, and intestine.
so roosevelt was able to win more than two terms because there was not yet a formal term limit on the presidency and the unique conditions when he ran for his third and fourth terms made his arguments for breaking with tradition acceptable to a majority of american voters
It was only  after FDR was elected for a fourth term that in 1947 Amendment 22  to the constitution was passed by Congress limiting the president  to two terms of office. Amendment 22 was finally ratified the  required number of states in 1951.