There could be a few reasons why your rabbit is breathing fast while lying down. One possibility is that your rabbit is having a respiratory infection. Respiratory infections are common in rabbits and can cause them to breathe rapidly as they try to get enough air.
If you think your rabbit may be experiencing hypoglycemia, you should take him to the veterinarian right away. Untreated hypoglycemia can be fatal.
There are other potential causes of rapid breathing in rabbits, such as heart disease, liver disease, or intestinal blockages. If your rabbit is exhibiting other symptoms along with his rapid breathing, it’s best to take him to the vet for a diagnosis.
If your rabbit is otherwise healthy and just happened to start breathing rapidly while lying down, there’s no need to worry. This could be a sign that your rabbit is simply feeling relaxed and comfortable. Still, if you have any concerns, it’s best to check with your veterinarian.

FAQS
Q: My rabbit has been breathing rapidly for a few days now. Should I take him to the vet?
A: If your rabbit is otherwise healthy and just happened to start breathing rapidly while lying down, there’s no need to worry. This could be a sign that your rabbit is simply feeling relaxed and comfortable. Still, if you have any concerns, it’s best to check with your veterinarian.
If your rabbit is exhibiting other symptoms along with his rapid breathing, such as loss of appetite, weight loss, or seizures, then you should take him to the vet for a diagnosis. Some of these symptoms can be indicative of serious illnesses, such as hypoglycemia or heart disease, and require prompt treatment.
Q: What is hypoglycemia and how can I tell if my rabbit has it?
A: Hypoglycemia is a condition that occurs when blood sugar levels drop too low. This can cause rabbits to breathe rapidly, as well as to have seizures or lose consciousness.