To dream that you are dissecting something suggests that you are trying to get to the core of some situation. You are trying to peel away at the layers in order to get to the heart of the matter. Alternatively, the dream may indicate that you are overanalyzing a situation. Consider also what you are dissecting.
In particular, to dream that you are dissecting a frog indicates that you are trying to figure out if the guy you are interested in is just a frog or is a real prince. Alternatively, the dream seeks to bring you back to your high school science class and how you felt when you had to dissect a frog.
To dream that you are dissecting a human cadaver suggests that you are trying to reveal or expose an aspect of yourself that you have kept hidden.