Normal? Uh, that depends.

Did your traffic go up by a huge amount too, say 15 or 20 times as much traffic?

No the traffic has been the same pretty much the same every day its just this one day i got all these clicks and cant work it out.

on the 18 September 2006 i got 12 clicks
19 September 2006 - 643 clicks :S
20 September 2006 - 8 clicks

That kind of a jump in clicks with no corresponding jump in traffic would worry me.

Do you have logs or site stats you can look at to see if you had a shift in your traffic source for the day? The same traffic numbers but a shift in source could have an effect. Still, that's a big jump in clicks.

have you made changes to banner placement on your site

I had this as well and informed adsense immediately after which they informed me they would check the clicks on my site to see if it would happen again. Of course you will loose the clicks which are not koosjer... Do it as well, it will prevent them from thinking you are frauding and shows you are doing things in good faith.

Quite agree. Notify adsense immediately. Obviously this massive jump in clicks is not normal. I assume you haven't told friends and family to click on things - and don't have someone trying to do you a favour by clicking. If you notify gooogle, at least it will be apparent that you are aware that there is a potential problem.

I had what looked like a click attack and sent off an email to Adsense support immediately, reporting it.

Possibly a competitor is trying to get you banned.