It is possible that Milu is breathing rapidly due to pain, falling from that height may have left Milu with some permanent injury which occasionally causes some pain; however without examining him I cannot say with any certainty. You should continue to monitor him and look out for any other symptoms, but any head trauma may present with issue later on in life. Regards Dr Callum Turner DVM
Regardless, you should visit your Veterinarian or an Emergency Veterinarian to examine Gizmo since she should be eating and drinking normally after this routine surgery and the ‘seizure like’ activity is also concerning; the moderate increase in respiration may be due to discomfort from surgery or due to something more serious. Regards Dr Callum Turner DVM
Rapid breathing (tachypnea) is a respiratory disorder characterised by abnormal breathing that is rapid and shallow. It is caused by a reduced level of oxygen, mechanical disorders (where the lungs aren’t able to expand as they should, usually due to a build-up of fluid in or around the lungs), and physiological disorders in which the cat’s respiratory centre in the brain is over stimulated.