Thank you for your question!
Rabbits intestinal tracts are extremely sensitive and will often become static (not moving) for a number of reasons. These include stress, dehydration, changes in diet or pain from an underlying condition such as dental disease.
The causes you mention in your question could certainly be factors in why your rabbit is sick but there could be other reasons. Often the first thing you may notice in a rabbit with gut stasis is a loss of appetite but the other thing to watch for is whether or not your bunny is passing regular faecal droppings. If your rabbit stops eating or producing faeces then that is an emergency situation needing immediate veterinary help.
There are other causes of weight loss so your vet will likely ask you questions about your rabbits diet, examine his teeth and possibly perform tests to rule out any other organ dysfunction. From there your vet can develop a treatment plan to help your bunny get back to good health.
-Dr Alex Hynes