Happened again last week

Last weekend a large majority of my successful keywords (5% and higher CTR) suddenly became inactive and had a min bid of .20 and .30 cents. I read everything I could on Google's site about how to "optimize" my campaign, ended up removing several 1000s of keywords that had never gotten any, or just a few clicks over the last 9 months, and as of yesterday morning, saw the min bids drop back down into the single digit range, as they've been for the last 9 months or so.