Gmail Contacts – Recover Accidentally Deleted Note

Gmail support states -

I want to retrieve my deleted account

Residual copies of deleted messages and accounts may take up to 60 days to be deleted from our active servers and may remain in our backup systems for an additional period of time. If you delete your Gmail address but wish to have it back, we work to help you recover your deleted accounts whenever possible. However, within a few weeks' time, accounts are usually no longer retrievable. Note that a successful recovery will only recover the username associated with the account.

That means even if you contact Google support and recovers your Gmail account, you won't get your mails back. Either way, your only hope is to mail Google support and ask for their help. And I hope it hasn't been much long since you deleted the account.

I don't know how Gmail operates in the browser, buy I assume it's a mix of HTML and Javascript. Some of that may have been cached at some time (and it's not at all sure that that included your mail text). Depending on your OS, if you remember unique keywords from that mail, you could try a search through all files in the cache directory and a search through free disk space with a file recovery tool (Google e.g. "search through erased file space" to find some). Your chances are slim, and any disk writes that have occured/are occurring on the disk make them even smaller, so boot that machine from a CD.