Lethargic bunny, but eating normally

Question
QUESTION: Hi Christine

Over the last couple of days my 4 year old castor rex house rabbit, Martha (doe) has become unusually lethargic. She is normally very hyperactive and inquisitive but the last couple of days she has been lying down a lot and looking a bit sad. She is eating and drinking normally, and her droppings are also normal in frequency and consistancy. She lives with a male rex (both neutured)and has done for the last 3 years, so she is not lonely, she has lots of new toys so is not bored either. I read about GI gas but he stomach does not seem to be bloated and is not making any noise.
I wondered if she could be cold as our heating is broken at the moment so i put a hot water bottle in her pen and she did go and lay next to it straight away. Is this also a sign of illness?
Any thoughts and advice much appreciated.

ANSWER: Bunnies are sensitive to temperature. Its quite possible she was just cold, so this doesnt sound like an illness. What was her activity level like after you put the heat source in there?

---------- FOLLOW-UP ----------

QUESTION: Just the same unfortunately. Left her with the hot water bottle over night and she was still lethargic this morning. It's a dramatic change in demeanour for her as she is normally so active which is why I am worried

Answer
Hmm... Any chance she might have injured herself? Perhaps an overly-excited binky and maybe she pulled a muscle?

As for the GI inquiry, you should actually hear some sort of gurgling and bubbling in there as their gut should be constantly moving hay through her system, so I might also suggest feeding her some critical care as well.

Does her mate avoid her? That would suggest there's something wrong. If he still snuggling up to her then she may just be having a "down" couple of days. If she really is having an issue, normal bunny behavior would dictate that all other buns would isolate that one as it would be seen as the "weak link".