The "emergency blood test" is something I had done as well, but it was right after takedown. The reason why it's called an emergency blood test is because low potassium is a dangerous situation for your heart. When my emergency test results came back low they came in with liquid potassium. It's deep red and looks like blood, and it has an awful taste, but the nurse looked at me gravely and told me to drink it up. They do not IV it because low potassium or a jolt of too much potassium can cause cardiac events.
Were you given any dietary restrictions for the test?
If not, I would eat a banana for sure, that will help. Low potassium is not good for you.