Hello,
I recently started having pain in one of my teeth (molar). I went to the dentist - x-rays taken, found a "cavity." Drilled and cleaned; put in temporary filling. It turns out there was no hole on the outer enamel and no decay; my tooth was just "mushy" inside. Doc said it was "self-absorbing...." or something. Anyone ever heard of this?

It could be as Compadre says, however there is a condition known as "internal resorption" where the tooth is destroyed from the inside out. It is not a common condition, but does happen.