This may sound strange (and perhaps a little amusing), but I've always
had an extremely sensitive belly button / navel.  In fact, the last
time I received a physical, I unconsciously lunged at the doctor's
hand when he was prodding my abdomen.  (Imagine your most ticklish
body part and times that by ten.)  I want to keep my belly button
clean, but the pain/sensitivity is nearly intolerable.  Is there a
name for this disorder?  Are there major nerve endings behind my belly
button?  Was some kind of mistake made when my umbilical cord was cut?
 Where do I begin to seek treatment?  Can you provide a top-ten list
of doctors in this country who can fix this problem?  Thanks in
advance!

I have the a similar problem. For me my belly button is very painful
when touched inside and oddly ticklish at the same time. It can make
me nausious. It began when I was pregnant with my last child though,
which is different than your case. Once my daft husband playfully
poked my navel when I was 7 months pregnant and I reacted as if I had
been punched. Thats about the time I noticed it. The doctors I have
mentioned it to havent paid much regard to it, so I assume it isn't
anything bad. If you hear anything more on the subject, let me know.

How very curious. I suppose your navel is hypersensitive because
nerves in that area are highly dense, perhaps just by chance. Maybe
specific types of nerves.

In relation to your umbilical cord, I assume "you've always had..."
this condition and it may be related.

Here's a point: Can you trigger the reflex yourself? A person can't
normally tickle themselves - a university study (Harvard? Standford?
Something...) concluded your brain knows if an action is
self-inflicted.

And how does the relfex work? Most reflexes work defensively, jerking
away from the stimulus. You might want to examine the reflex closely,
seeing what muscles are triggered and such.

This is all speculation and ponderings, useful only because it comes
from another person's view.

~Falos