If that could be the case, just slowly reduce the water. The leaves will yellow and dry as the plant goes dormant. When new growth begins in a few months, resume watering and place it back in its bright spot to bloom again. When the bloom crop becomes small and sparse, replace it with a vigorous new plant or bulb. It may be too wet.
Gloxinias are susceptible to crown rot which is often caused by wet, soggy soil.
This can also be the result of using cold water. Gloxinia leaves are very brittle, and since they are so large, it's easy for them to be damaged by careless handling. If the leaves are also sticky, look for sucking insects such as aphids. They can be treated by spraying the plant with insecticidal soap. See Bachman's information sheet Indoor Insect and Disease Problems.