Are you T1D or late stage T2D, Gravy?
Insulin lowers plasma kalium, the Ikr channel is inhibited in the myocytes. It can lead to reentrant arrhytmias. You might also feel angina pectoris because of the positive inotropic effect due to the natrium channels being given more time to recover - thus more can open in the event of depolarization, contraction force is greater. The frequency is reduced as the membrane potential is lowered, hyperpolarized. Basically the effect digoxin would give too, albeit that's from the na-k-atpase inhibition.
In short: insulin usage should be monitored - it has other effects than the, logical, lowering of blood glucose via glut4 channel up regulation.
Here is the always trustworthy wiki link for you (or get rang&dale or basic pharma, who cares).
http://en.wikipedia.org/wiki/Hypokalemia#Pathophysiology