That is an excellent question and one that is best answered by your primary care doctor
who will best be able to get a good physical examination and also check out your teeth and find out if there is something concerning based upon the symptoms you had of having teeth that felt loose. In general, trauma such as a fall may cause teeth to become loose, but it doesn't sound like you have had any trauma to your face or teeth. Severe gum disease can also cause loosening of teeth, but it doesn't appear that you have that as you have seen a dentist recently that said that your gums are ok. It is likely based upon your history and the fact that it sounds like you take good care of your teeth, it is possible that this was just a random fluke, but that being said, it is still really important that you are evaluated by your dentist as there could be something more serious underlying this and it is important that something serious is ruled out early otherwise it could progress quickly. In the meanwhile, continue to floss and brush your teeth as directed by your dentist.