These sort of emails use harvested addresses, they could have come from a website you visited/ registered at. or from a friends address book. The originator of the spam email uses harvested addresses to spoof the senders address.
Its the same as you sending an email from home, but changing the sender address to your work email address, except the spammer has a bot that randomly changes the sender address.
Your account most likely hasn't been hacked/compromised.