Periodontitis is severe gum infection that cause loose teeth and tooth loss. When periodontitis is left untreated, it can result in loss of the structures that hold the teeth, resulting in loosening of the teeth up to tooth loss, which can also cause problems chewing. Other consequences include the impact on general health as well as bad breath, shifting teeth, changes in bite and possibly even speech, which leads to self-consciousness and embarrassment.

The most common reason for tooth to get loose would be gum disease. Highly suggest you consult a Periodontist(Dentist specialising in gum diseases) regarding the same to prevent more teeth from getting loose.

Tooth doesn't fall on its own. Definately there is gum and bone related problem that has been overlooked for years and now they have loosened. You need to get yourself checked before anymore tooth get lost. Natural tooth is always precious and nothing can give you the strength original tooth has.