The duration depends on the cause. Many common bugs, including viral ones like norovirus, cause intense symptoms for 1-3 days that then settle. Some bacterial infections can last longer or cause more severe illness, and certain parasites can persist for weeks.
While recovering, focus on fluids and rehydration salts, rest, and bland foods once you can eat. Avoid preparing food for others and wash hands thoroughly, as many causes are very contagious. Stay off work or school until at least 48 hours after symptoms stop, where that guidance applies.
Contact a doctor if symptoms persist beyond about a week, keep returning, or followed foreign travel. Seek urgent care or call your local emergency number for warning signs: blood in stool or vomit, high fever, severe or worsening abdominal pain, persistent vomiting preventing fluids, or dehydration signs such as dizziness, very dark or little urine, and confusion.