Question
why did all the leaves and flowers fall off of my potted bouganvilla?

Answer
I can't tell from here what conditions the plant is exposed to. Usually extreme changes in a plant, is the result of extreme changes in the environment, either soil, conditions, such as dry, wet, fertilizer, temperature, etc. or air, such as humidity, temperature, and drafts.

A common cause for complete leaf and flower drop is a condition called Crown Root or Stem rot. It is commonly caused by over watering, especially in winter, when the plants are dormant, and do not need much moisture.

Check the plant over carefully, both in the soil, and the stems. Look for decay, or discoloring. If the plant has signs of this, discard it.

bakerplanter