Loose stools last 24 hrs. no dietary changes and no other symptoms. is this likely from a minor gastrointestinal virus?

Diarrhea: Given what you stated, yes you could have a "24-48 hour" bug. Have you been in contact with anyone else with similar symptoms? Eat or drink anything "new" to you? The main thing is to make sure your fluid intake is adequate. If not better in a day or two call your primary care physician. If symptoms worsen such as pain or seeing blood in your stool; GO to the emergency department.