Someone manage to break into your mail account and stole the contact list. Anyone can use a stand alone email program to send mail with any from address. It is now too late for you to do anything other than change your password. They already have the contact list.

₪ ʎəɿʞɹɐq ₪

Relax? Your e-mail likely didn’t send it. Unfortunately, your address was ‘harvested’ by a spam bot either in your computer or a friend’s. Of course, you should immediately change your password, but that isn’t the most likely cause of this.
First – you should run a Deep Scan for viruses in Safe Mode first (Hit F8 frequently immediately after re-booting, then select Safe mode using the arrow keys and Enter. Running you anti-virus more than once is tedious, but helpful. Some spyware can be detected that way, but not all. Some spam bot programs can disable the anti-virus program you run, even though you think you are protected. You may need to download an anti-virus program on another computer and run it directly from a flash drive once it has been updated, of course. (That’s what friends are for!)
Second – download and install, then run Trend Micro’s Housecall online scanner. You need to open an account, but that’s a small (free) price to pay. It detects many root-kits, trojans and other spyware as well as viruses. Since some spyware blocks downloading of security programs, I would recommend using another computer and a flash drive to install any programs such as this. You can also run these programs directly from the flash drive, but remember to update the files first.
Thirdly – remember all those people who don’t clean out the e-mail addresses as they forward mail? And those who send everything in the open instead of as BCC? They are the ones who are responsible for your addy having been harvested. You DO know how far an e-mail address can travel as mail is forwarded (oh, the horror of those ignorant of ’safe mail sending’!)
Fourth – contact all you know in your contacts list who are guilty of poor habits and remind them how to send mail safely ( some are just learning, and may not even know what BCC means – or they are bone lazy or too rushed to care)
Fifth – contact your list and apologize that you have been harvested and will open a new account soon.
Finally, solve the problem once and for all time – open a new e-mail account in a new name, and pass it on … promising the guilty parties that you refuse to send them mail until they are reformed – and follow through! (Of course, you’d use your compromised account for this)