Answer:

When you initially placed your right hand in the cold water, cold thermoreceptors in your hand fired creating signals that, after being processed in the brain, enabled you to label the water as "cold." As the left hand was put in hot water, warm thermoreceptors initiated signals, allowing you to identify the water in this pot as "warm."

After awhile the thermoreceptors in your hands quieted down. They became desensitized and the water in the respective pots did not feel as cold or as warm anymore.