Heat stress is basically the early stages of heat stroke. It's when the rabbit starts to get mildly overheated. Heat stroke is when the core body temp gets too high and serious cell damage can occur, sometimes irreversible. It's a fine line between heat stress and heat stroke, and if there is any doubt if your rabbit has heat stroke, you should err on the side of caution and get your rabbit to your vet immediately.
Heat stress, beginning of heat stroke:
http://www.annarbor.com/pets/keeping-our-rabbits-cool-during-the-heat/
Heat stroke:
https://www.petcoach.co/article/heatstroke-hyperthermia-and-overheating-in-small-pets-signs/
So giving electrolytes may be helpful if they haven't been eating and drinking very well due to heat but are still only in the early stages of heat stress. It's also essential to get them to a cool place to help reduce their body temperature. Just giving electrolytes doesn't solve the problem and the rabbit can continue to become overheated.
Glucose is a necessary sugar in living things for proper cell function, including rabbits. As with us, it's better to get it from complex carbs in our normal diet. But there are times when it's needful to consume or receive sugars that are quickly absorbed, such as someone suffering from hypoglycemia, or during strenuous exercise when we may get depleted quickly.
Normally rabbits won't have a rapid depletion of glucose from their blood, but there are times that it could happen, such as a rabbit experiencing heat stress when they haven't been eating or drinking normally, a rabbit suffering from diarrhea and not getting the needed nutrients and fluids from it's digestive tract because it's loosing them through the continued diarrhea, or they can even get low blood sugar during non obstructive GI stasis, or other times of stress.
But overdoing the sugar is also not good for rabbits either, as we know it can affect the microbial balance in their digestive tract. I can't see that occasionally giving electrolytes in the
appropriate situation, would be a problem or harmful for most rabbits. As rabbits that are given fruit also get sugars, so not much difference, just needs to be limited and sparingly, and not be given when a rabbit has a sensitivity to a lot of sugars, has a complete obstruction, has bloat, diarrhea, other digestive problems where sub q or IV fluids would be the appropriate route, or has kidney problems. But for someone inexperienced at deciding when it is appropriate, it would be best to consult their knowledgeable rabbit vet. I'm not a vet, I'm only relaying info that I've learned and what I might do. When in doubt, always consult a knowledgeable rabbit vet.
