Certified GKH Gardening Expert
I am concerned about the container. Are there any drainage holes? A cactus must have well draining soil. If it's in a cache pot, a pot within a pot, that is fine, as long as you remove the inside container to water and let drain before returning it.
If it looks like it's not getting the water, it may have root rot. When the roots can't take up the water, the plant suffers. Try repotting it in cactus soil, and make sure your container has drainage holes. Let the soil completely dry before watering again.