Bloat, which is distention and blockage of the stomach, occurs for unknown reasons in some dogs. Signs include a distended abdomen, dry heaves, increased salivation, and depression. The dog may repeatedly lie down and get up, pace, whine, or stretch. Bloat is a surgical emergency. It can't wait overnight.
Urinary obstruction is fairly common in cats.
Straining to urinate should not be confused with constipation. A cat with urinary obstruction will rapidly get worse and needs to be seen by your veterinarian. An animal in seizure needs to be protected from hurting itself. A seizure can be a slight loss of muscle control or can be severe, with the animal paddling on the ground completely out of control. An animal will lose bladder and bowel control, be mentally unaware of its surroundings, and appear dazed after a seizure.