A 52-year-old woman is taken to the hospital because she has become completely paralyzed. By the time she is examined, the paralysis has begun to clear, and it has completely resolved an hour later. She states that she has had previous episodes of severe transient weakness, but that this was the first time that she felt actually unable to move. She has also been experiencing paresthesias. On physical examination, her blood pressure is 160/100 mmHg. Blood tests reveal serum a sodium of 155 mEq/L, potassium of 2.8 mEq/L, and decreased serum renin. Which of the following is the most likely diagnosis?