Deleting my entire chat and composer history fixed my Cursor window lagginess (I also killed/restarted all my in-window terminals before this as the first attempt).
There were a few items that took a while to delete. And clicking delete on one specific recent one lagged the window out for about a minute (it was a long convo, though some others were too).
TLDR deleting all my Cursor chat/composer histories fixed immense cursor window lag.