I have hyperemesis, if I get too dehydrated I need to go in to get fluids. If you have ketones in your urine you also really need the IV to be able to flush them out your system though you technically get them when your body is in starvation mode
So depends if it's a short term bug or HG and how long it's been. Once you get IV fluids you should feel a bit better, in combination with the anti sickness medication I was able to start hydrating myself, was recommended lucazade sport as I still can't keep down plain old water and get essential electrolytes and glucose from the lucazade, has to be the sport one not the fizzy one but I suppose you need to be able to find your 'safe' drink to be able to get rehydrated properly so drink what you are able to keep down.