Cardiac arrythmias are common with hypothermia. The stress of standing up can cause orthostatic hypotension, which in English is a drop in blood pressure caused by standing up (this doesn't require hypothermia). A sudden drop in blood pressure combined with an electrically compromised heart doesn't sound like a good thing. I'm not knowledgable enough to take us from long Q-T intervals plus sudden hypotension to V-Fib, but the latter would kill you pretty well.