Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your situation, and wanted to help.
I share your concern about Miss Bunny.
As a prey species, rabbits instinctively hide illness until it is quite advanced (since not doing so would make them a target for predation). That means even if she is giving no specific signs of illness, we need to tread with care. So, if she is not acting like herself, subdued, and possibly hunching when sitting under the table, it'd be prudent to have her checked by your local vet. Ideally, we'd want them to listen to her lungs to make sure there is no lower respiratory tract infection brewing (this can reduce their activity since it can reduce oxygen intake); check her belly for any blockages or obstructions; rule out any fever, and pinpoint what may be suddenly slowing her down. Based on their exam findings, they can help guide you on what is lurking and start treatment to get her back to the bouncy, wild gal she usually is.
Just in case you do not already have a vet for her, you can find one via the Rabbit Vet Database (http://rabbit.org/vet-listings/), AEMV (http://www.aemv.org/vetlist.cfm) or http://www.guinealynx.info/vetlist.html (since cavy vets usually see rabbits too).
Please take care,