hi sir/madam, There are many causes for this.i will give you some knowledge about this now. 1.Food allergies:- Certain foods, like shellfish, nuts, or eggs, can fool your immune system into identifying them as harmful foreign invaders. When you eat one of these trigger foods, your immune system launches a series of events that leads to the release of histamine and other chemicals. These chemicals produce allergy symptoms, which can range from hives and mouth swelling, to nausea. 2.Food poisoning:- Food that sits around for too long or isn’t properly refrigerated attracts bacteria, viruses, and parasites that can make you sick. Food poisoning symptoms like nausea, vomiting, and diarrhea, typically start within a few hours after you’ve eaten contaminated food. 3.Stomach virus:- This common bug, which is sometimes nicknamed the “stomach flu,” infects the intestines and triggers gastrointestinal (GI) symptoms like nausea, vomiting, and diarrhea. You can catch a stomach virus by getting too close to someone who’s sick, or by eating food or drinking water that’s been contaminated with the virus. 4.Pregnancy:- One of the earliest signs that you’re pregnant is an uneasy, queasy feeling, which often starts during the second month of your pregnancy. Changing hormone levels trigger pregnancy nausea. 5.Acid reflex:- A burning feeling behind your breastbone, known as heartburn, is the hallmark symptom of gastroesophageal disease (GERD), but this condition can cause nausea, too. GERD happens when the muscular valve between your esophagus and stomach malfunctions, allowing stomach acid to leak up into your esophagus. 6.Anxiety and stress:- Stress doesn’t only take a toll on your emotions. It affects your physical health, too. A difficult breakup or job loss can make you lose your appetite, or feel sick after you eat. The nausea should let up once you get your stress under control. 7.Cancer treatment:- Some chemotherapy drugs cause nausea as a side effect. The nausea should go away after you’ve finished the treatment. 8.Gallbladder disease:- Your gallbladder is an organ that sits in the upper right side of your abdomen. It helps your body digest fats. Gallstones and other gallbladder diseases can affect your ability to digest fats. As a result, you’ll feel sick to your stomach, especially after you eat a rich, fatty meal. 9.Irritable bowel syndrome:- IBS is a collection of GI symptoms, which can include abdominal pain, diarrhea, and constipation. Nausea is one of the most common complaints in people with IBS. 10.Motion sickness:- Some people are especially sensitive to movement. If you’re among them, the motion of a moving vehicle will make you feel sick. Eating before or after your ride can make the nausea even worse. If you have following symptoms consult a nearby doctor soon:- 1.Blood in your vomit or stools 2.Chest pain 3.Confusion 4.Diarrhea that lasts for more than a few days 5.Extreme thirst, little urine production, weakness, or dizziness, which are signs of dehydration 6.Fever of over 101.5°F (30°C) 7.Intense pain in the abdomen 8.Rapid heartbeat 9.Severe vomiting or trouble keeping food down As a ayurvedic doctor i would like to give you some Tips for prevention:- 1.Suck on ice cubes or crushed ice. 2.Avoid greasy, fried, or spicy foods. 3.Eat mainly bland foods, such as crackers or toast. 4.Eat smaller meals more frequently, instead of three large meals. 5.Relax and sit still after you eat to give your food time to digest. 6.Eat and drink slowly. 7.Serve foods cold or at room temperature if the smell of cooked food makes you feel queasy. Hope i was helpful,stay healthy eat good food,do yoga and meditation it will help you a lot. have a good day