I posted my reply in your other post, I'll copy/paste what I wrote here:
I'd def take it out of the cage and isolate it from your other two buns. Bring it inside and put it in a warm, quiet place so you can more closely evaluate it.
Its possible that it ate something toxic, are you also feeding pellets/hay? I have Kelp powder on hand for any sort of toxin poisening, but I *think* a Vit E liquid capsule may be a substitute, you'd have
to google it though. You'd have to google toxic plants in your area, I'd be careful feeding anything you don't know what plant it is.
How do the other two bunnies look? How long have you had the bunny, and did you quarintine your new rabbits before you put them in with the other bunny? I'd def take that LH doe out before the other bunnies breed her,
unless of course you have all does, and even then they may start to fight and kill the smaller bunny once their hormones start in.
Take it out and look over it, listen to its breathing (does it sound congested?) Check its poop (Is it runny? Is it pooping?) Check its belly, does it look bloated?
Run your hand down its back, does it feel spiney? Check its teeth for malclusion and its legs for breaks at the hock (or sore hocks)
Is it *rolling* like they would with Wry Neck? (Check its eyes for rapid back and forth movement)
If you have Pedialyte on hand or some other electrolyte that would not be a bad thing to give it, might help perk it up.
Rabbits being prey animals they often hide that something is wrong until its bad, unfortunetly. A lot of the signs of a problem are really subtle.