Is it normal for a tooth to fall out of a set of full dentures? (Photo)

This is not uncommon, especially if the denture is older.  See a dentist and they should be able to place it back in the denture with an acrylic material.  Good luck.  

Denture acrylic sometimes chips and teeth can occasionally come out of a denture. This is not a difficult repair to make, some dentists might repair it in their office. I prefer to have a lab do a processed repair when possible, at worst she might be without the denture for a day or two.

It is not unusual for a tooth to come out of a denture.  It is an easy repair for the lab or the dentist to do.  Just remember, God's teeth did not last your lifetime, how can we expect the ones we make to do the same?