This strange sensation has a very serious medical explanation.
If you have also felt this funny sensation when you touch your navel, here is the explanation behind it at last!
It is provided by Dr. Christopher Hollingsworth, a member of the NYC Surgical Associates. ‘The navel stimulates not only the skin, but also the fibers of the “inner lining” of your abdomen, so when you put your finger in your belly button, it sends a signal to the deeper fibers in the abdominal cavity and to your spinal cord. Your spinal cord at this level also transmits signals coming from your bladder and urethra; it's almost the same sensation, and you interpret it as discomfort in your bladder.’
This nerve response is therefore read by your body as a need to pee, which then transmits this unpleasant sensation. You learn something new every day!