First, read the English article below.

Patients with gastritis often experience "epigastric pain," or pain in the upper central abdomen. It can be described as a burning, gnawing, or deep boring pain. You may find that it wakes you up in the middle of the night, but it can often be relieved by eating something or taking an antacid. These symptoms are fairly common with gastritis. You may also see blood or bile in your vomit. The blood may be partially digested and look like coffee grounds. This is caused by bleeding ulcers. You should contact a doctor immediately if you see blood or green bile in your vomit. Excessive vomiting can often lead to dehydration, which can also be dangerous. Make sure to get a lot of fluids if you're vomiting. The black, tarry stool seen in many gastritis patients is called “melena.” The same bleeding ulcers that makes people vomit blood causes them to excrete it through stool. This should also be reported to the doctor as soon as possible. People with gastritis often find that they've lost their appetite. You may lose your it altogether or simply find that you feel full after a smaller amount of food than usual. Take notice if your clothes feel unusually loose without any explanation. If you're losing weight without purposely dieting, you may be eating less. If your appetite decreases significantly, you may eat little enough to be considered anorexic. See a doctor if you feel woozy or dizzy from a lack of nutrition or fluids. The inflammation in the stomach lining causes gases to build up. This, in turn, can make you belch more than you usually would. Even with the release of gas through burping, you may still feel bloated from all the gas that’s trapped in your stomach. 

Now, please write a short abstract for it in Vietnamese. Abstract:
Lưu ý dấu hiệu đau bụng. Lưu ý dấu hiệu buồn nôn và nôn mửa. Lưu ý dấu hiệu phân đen như hắc ín. Lưu ý sự thay đổi khẩu vị. Lưu ý tình trạng ợ nóng hoặc đầy bụng quá mức.