It is possible that there might be a physiologic reaction that can cause some concern for an owner observing the death. The pet might go into an excitatory phase where there might be muscular movement. Also, the sphincters may relax and the pet might urinate or defecate. In addition, animals may not close their eyes at the time of death. These activities are not indications that your pet has suffered pain.
Some owners opt to be with their pet until the end.
Other owners don't want to be in the room. If you want to be present, you should be present. When people die, autopsies are done to confirm cause of death. Your veterinarian may ask you if you want a necropsy-a pet autopsy. If your animal is dying of an undetermined illness, it may be comforting to request a necropsy.