A person with healthy kidneys is unlikely to have too high potassium levels - there's a built-in control which allows the kidneys to excrete excess potassium if there's too much.
Unfortunately there's not such a control to prevent levels from dropping too low
That being said, you're likely to experience other symptoms first, such as overall muscle weakness and fatigue before heart arrhythmias occur. If you're losing a lot of potassium over a short period of time, such as with vomiting and diarrhea, then it's more serious, and a trip to Emerg is in order.
Certain medications can cause the kidneys to retain potassium, so levels might build up .. ACE-inhibitors for heart/blood pressure such as enalapril and captopril, potassium-sparing diuretics such as spironolactone, and sulfa antibiotics esp. Bactrim (Septra). Check with your pharmacist before taking supplemental potassium.
Actually, disturbances in heart rhythm are more likely related to low MAGNESIUM levels. Magnesium is also lost in the urine along with potassium, and levels may drop with ketosis when there's increased water losses. Diabetes, high blood sugars, high insulin levels can also deplete circulating levels of magnesium.
Adults require 450 to 500mg per day of magnesium; you can usually find it combined with calcium in a ratio of 333mg Cal : 167mg Mag. Take 3 a day, with the last dose at bedtime.
Doreen