Well, click bombs resulted in many account terminations over the last few years, maybe someone is bombing you really.
yes, there's nothing wrong if you will email google about this activity.. Also, as long as you didn't click your own ads, I think there's nothing much to worry..
sometimes ctr can be too high, if you have good visitors coming from search engines and your traffic do not include bots etc. then you can be safe. however if you are still worried just remove the ads for a while and then re-insert the ads code.
Just drop Google AdSense an email, You can also add a new post in AdSense's official support forum as a proof in case of trouble. dont use 3 day per page use one
I think it is better to just drop an email to google adsense support to notify about your situation and tell them that you don't have any idea at all why this is happening.
Depends on your traffic too. If you are getting 2 impressions and 3 clicks, then nothing to worry. However, if you are getting 10k impressions with more than 10k clicks, then it is dangerous