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Your plant may be affected by root rot.  A holiday cactus with root rot displays wilted, limp, sagging growth, but an inspection of the roots will tell the tale. Remove the plant gently from its pot. If the cactus is affected by rot, the roots will display blackened tips. You can save your Christmas cactus from root rot if you identify the disease early. If the fungus established itself in the roots of your Christmas cactus it is not possible to save the plant.  If the plant is suffering from root rot, get rid of the soil. Do not plant any seedling in that pot unless you sterilized it. Repotting Christmas cacti in organic, humus-rich soil is important. They also grow better when they are “pot bound,” which means the container and root system are about the same size.  The holiday cactus needs ample humidity, especially when grown in the dry conditions of heated homes during the winter. Feed your holiday cactus monthly with a half-strength, diluted water-soluble fertilizer during the early spring and summer months. Once you've noticed the formation of flower buds—usually late summer or early fall—stop feeding. After the plant blooms, you can resume monthly feedings.

References
How to care for and reflower your Christmas cactus - MSU Extension
The secret to getting a Christmas cactus to bloom: temperature and light - MSU Extension

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Good Morning,
The Christmas cactus doesn’t need fertilizer while it is blooming. From April to October, fertilize Christmas cactus every two to four weeks as new leaf growth begins. Christmas cacti need extra magnesium, so mix 1 teaspoon Epsom salts (magnesium sulfate) per gallon of water and apply it every other watering – not at the same time as fertilizing. Stop fertilizing in late September or early October to encourage flower bud production.

Reference
What Fertilizer Is Best for a Christmas Cactus? (sfgate.com)

Good Luck!!