Non-spayed, middle aged female pets can develop a uterine infection called pyometra. Pyometra occurs within 2 months after a heat cycle and often results in discharge of pus from the vagina. The pet may frequently lick the vagina so discharge may not be seen. Dogs develop pyometra more often than cats. Other signs may include PU-PD and depression.
Liver failure causes vomiting as well as other signs depending on the type of liver disease.
Bladder obstruction will cause a sudden onset of vomiting. Bladder obstruction is fatal in just a few days. Bladder obstruction or rupture will cause a sudden onset of vomiting. The urethra that leads from the bladder to the outside can get plugged by stones or tumors. The animal will strain and pass just a free drops of urine or none at all.