Thnx for your reply.
The reason I mention about the 728x90 is because according to google reports, its the main money maker for my sites. The other reason is I mention the tablet thing is because when you look at my site via the tablet, you still see the arrow buttons in the adsense units where as on a desktop the arrow button is not there anymore and the font is very very small. (it never used to be like that). For now i have removed the ad unit, but it just seems very strange that this started to occur the last 2 days. Since January I have had average 700 to 800 clicks. Yesterday and day before 200. Relevance has always been an issue, but I stil got 700-800 clicks even with irrelevant ads. I am 100% certain google is up to something with that ad unit when viewing from a pc. Its clear from the reporting tool.