My mum always salivates whenever she finish eating so she have sweets to stop it or else she throws up. it always happens. what's wrong with her?

Conditioning..: Somehow she has conditioned her body to respond to having sweets after meal..It is an autonomic nervous system response. There was a famous russian physiologist pavlov who trained dog to salivate at the sound of the bell...In her case, her gut learned to expect sweets with her meals. She conditioned herself to do so, without even knowing it. Check out pavlov's classical conditioning... Good luck.

Your mom may have...: Gastroparesis, or slowing of digestion and emptying of the stomach. Hyper-salivation is a frequent precursor to vomiting. I would not give her sweets, but artificially sweetened lemon drops. The most common cause is diabetes, which may not be evident. She needs to eat smaller but more frequent feedings. If problems persist, she will need medical evaluation.

Strange story: Sugar usually stimulates an increase in salivation, not a reduction. This might be a question for either an ENT doctor (?Parotid or other salivary gland abnormality), or for a psychiatrist or psychologist. If your mom wants to change this she should talk to her primary care doctor and start things moving likety-spit.