Christmas cacti like an average temperature of between 15 degrees and 18 degrees celsius and don’t like sudden temperature changes.
If buds and flowers fall off the temperature has changed too rapidly or the plant has been overwatered.
Watering
Christmas cacti need more water than a normal cactus.
Once the compost has dried out they should be watered with tepid water.
Lift the plant and see if it feels heavy. If the pot feels heavy the compost is holding water so leave the watering for another day.
Shriveled stems are caused by the roots being damaged by under watering or over watering.
Maintenance
Remove all spent flowers as needed. Hold the stem and twist off the dead flower, taking care not to knock off the unopened flower buds that are beside it.