Why is my cat breathing fast while resting after flea treatment?

Rapid breathing can be caused by pain, stress, fever or overheating. If you struggled to catch and treat your cat, it is possible that you are seeing a stress response. If this is the case, your cat's breathing should start to slow down and return to normal once the stressor has been removed (i.e. You are no longer restraining your cat). If it doesn't improve or gets worse, your cat may be having an adverse reaction to the flea treatment. Some flea treatments that contain permethrins and pyrethroids are toxic to cats, so check the packaging to see what type of active ingredients were in the flea treatment. If pyrethrins, permethrins, or pyrethroids are the active ingredient in the flea treatment, contact your veterinarian or go to a 24-hour emergency clinic immediately.