Remain as still as possible, however painful. Intense shivering and severe pain are natural body reflexes in cold water which will not kill you but heat loss will. Any person pulled from cold water should be treated for hypothermia. Once shivering stops, core body temperature begins to drop critically. Your goal in treating hypothermia is to prevent further body cooling.
Severe cases call for rewarming by trained medical personnel.
In all cases, arrange to have the victim transported to a medical facility immediately. In cases of hypothermia you should check very closely for as long as two minutes. Start CPR if necessary. Remove victim's clothing with a minimum of movement, cut them away if necessary. Lay victim in a level face up position with a blanket or other insulation beneath them.