"My theory here is that the pt induced his tetany and seizure activity through his recovery. By his own admission he had only been taking in water in the last 24hrs with no food, gatorade, etc. So while he was replacing his volume, he wasn't replacing his electrolytes. As a result, while his absolute electrolyte levels would not be continuing to decrease, his concentration would as his rehydration with flat water diluted the electrolytes effectively decreasing his levels and triggering the muscle spasms, tachycardia and seizures. Does this make sense or am I still missing a key piece?"
I like that you think outside of the box, but I think sometimes it is easy to over think calls like this.
Seizures can be weird, but in my experience, weird "seizures" usually aren't seizures at all. The tachycardia is interesting, but the fact that he is fully conscious and unable to unclench his limbs sounds like a case of bad acting.
Withdrawal seizures? It seems unlikely to me that a 24 y/o, even one whose been binge drinking, is going to have withdrawal seizures right after a night of drinking. Now, a veteran alcoholic who is drinking 24/7, then stops for a day or two, that's another story altogether.
Hyponatremia? No. You have to drinking a huge amount of water/beer to do that, and probably also have some underlying SIADH. He would also have a very depressed LOC.
Hypocalcemia? Doesn't sound like tetany at all, more like clonic activity. Unless you've had your parathyroid gland removed (can happen when being treated for tumor), it is really unlikely that you would get critically hypocalcemic. Not eating or not drinking, or binge drinking alcohol, will not cause hypocalcemia.
Best to just shrug your shoulders on this one.
