As a tangent, what causes the “tickling” sensation in my wee-wee (and has since I was a child, and apparently it affects my sons as well) when you are in a car and suddenly go over and down an incline at speed? We all call them the “whee bumps”. I used to get that same feeling when I would use a swing as a child, but no longer.
But the whee bumps still get me there.
…and this little piggy went whee-whee-whee all the way home. 
(couldn’t help myself)
I get a similar sensation going over bumps, but more in my bladder and lower abdomen, kind of like a brief feeling of weightlessnes. The bump has to be a certain size for it to happen. Too small, and it’s just a “bump;” too big and you really feel the car climbing and then descending.