ailing bunny

Question
Hi, I have a 3 yr old mini rex named Sun Top, and she is normally a very inquisitive and energetic bunny, but when I got home from work tonight she was very different.  She just laid down in her cage, and when I let her out she would just sprawl out on the carpet, and a few seconds later she would get up and move a few steps and sprawl out there.  this is very unlike her, and she also has been breathing much faster than normal, and her ears are constantly up.  she almost seems like she cant muster up the strength to move herself places.  she won't hop around more than a few steps.  Naturally I was alarmed by this, so I took her to the emergency veterinarian in town, and after a check up, they were unable to determine anything to be wrong with her, but they gave her fluids and electrolytes just to be safe.  she is still going to the bathroom, but I haven't seen her eat yet, and she will go to her water bottle, but doesn't seem to drink more than a drop or two at a time.  she is a strictly indoor bunny, and is the only animal in the house.  she just seems very frustrated and upset, yet fatigued at the same time.  my roommates let her out while i was gone and said she was acting normal, jumping on the couch and being sociable, so I don't know what could have happened.  she is like my little child and I can't stand to see her in pain, do you have any advice or insight for such a situation?  thank you so much for your help!
-kristen!

Answer
Is she spayed? 3 years old is about the time that unspayed females start to be much more succeptable to uterine and overian cancer. Cancers can be very draining on the body, causing fatigue.

It could also be a number of other things from a bad mood, to a small illness that went away, to a little bruising (maybe she jumped around and landed a bit funny).

Keep a close eye on her. If it goes away in a couple days, it was likely one of the minour problems. If it happens more often, you might want to take her in to a rabbit-savvy vet to have her checked out more thoroughly (as most regular vets are not very knowledgeable about rabbits). If she is not spayed, you might want to think about getting her spayed, too.