Hope you do not have this problem, as it spreads like wildfire from file to file.
Deleted Global Colors/[HUH?] error/Unused Brushes Keep Returning
Look for excessive items in any of the palettes that store styles (swatches, graphic style, brushes).
Create a new document with nothing in there and draw a few shapes, and copy and paste them if that is laggy, then good news is you do not have the nasty problem form the link above, but something else possibly related to a corrupted OOBE, preference or 3rd party software.