Participation in this study will last about 11 months. Participants will first attend a 3-day inpatient visit that will include a medical history, physical examination, blood work, heart rhythm testing by an electrocardiogram (ECG) and Holter monitor, strength testing, a health questionnaire, and daily potassium supplementation. Participants will also track the number and length of weakness episodes that they experience while in the hospital. On the last day of the inpatient visit, participants will be provided with multiple bottles containing either potassium or placebo. Participants will then return home for an 18-week treatment period that will consist of six 3-week-long treatments of either potassium or placebo, with the treatment schedule being randomly determined. Upon completing the first 18-week treatment period, participants will attend a second 3-day inpatient visit that will include the same tests and procedures as the first. The only difference will be that participants will receive acetazolamide along with potassium. This will be followed by a second 18-week treatment period that will consist of six 3-week-long treatments of either acetazolamide or placebo. At the end of the second treatment period, participants will fill out another health questionnaire. Throughout both 18-week treatment periods, participants will phone in daily to track any muscle or heart problems. They will also provide blood samples on a weekly basis. At Weeks 2, 5, 8, 11, 14, and 17 of both treatment periods, participants will wear a Holter monitor for 24 hours and then mail it in. A final outpatient visit will occur 8 weeks after the end of the second treatment period and will include heart rhythm testing, muscle strength testing, and blood work.