Removal from Google's Index - email notice from Google?

[Gracia]

This morning I've got an email from google advising me that my main site has/will be removed from index for at least 30 days. They did specify the reason - hidden text. And yes, my site had this hidden text for years, from the time when I put it online, when I didn't know much about search engines and google guidelines for that matter. This is my very first site and I didn't even remember that it had hidden text.
Anyway, I checked the headers and it looks like it's from Google. For now I got rid of the hidden text (the site doesn’t have any other guidelines violations) but haven't submitted a re-inclusion request yet, the site is still in the index but I don't know for how long.

If you had the same experience, would you have any suggestions, should I wait or should I submit re-inclusion asap? Is that possible to forge email headers so that it would look like it came from google? if it is I wouldn’t be surprised if it came from my competitors. If G didn’t send the email could a re-inclusion request hurt my site’s ranking? Any other info that could help me?

Thanks very much in advance.