This a phase 2 study comparing the efficacy of intravenous (IV) lacosamide (LCM) with IV fosphenytoin (fPHT) in controlling frequent nonconvulsive seizures (NCSs), the Adverse Events profile of LCM compared with fPHT when used to treat frequent NCSs, and length of stay in an intensive care unit for subjects treated with LCM versus subjects treated with fPHT. The trial will include a preacute-treatment period, an acute-treatment period, a postacute-treatment period, and a long-term follow-up period.