My email used as spam?

Well this evning I suddently got a lot of replies from my friends about some email/facebook message I haven't sent... There are no signs me sending the first email/message so..

Does anyone know how this works? Have people hacked my email or is there some way to send an email with my email-adress without having access to it? 

if it's FB, there's a virus that'll do that.

Thanks for the reply.

Will it go away or will it continue untill I do something?

I dunno if this is the same but I once clicked this fake video on facebook that automaticly shared the video to loads of my friends, I just manually removed them constantly and eventually it stopped...