HW, that email about Viagra might have been sent to everybody on your address book, including your own address. Check the time it was sent and to whom? One of my friends computers used to send out emails like that regularly at 5 am... I dont know how she stopped it, I asked her to delete my name from her address list. You might start by running your virus checker.
Bummer. I deleted it and never checked that. Can't get it back now.
Funny you should say that as for months I was getting a spam email from a friend on a regular basis. I asked her about it and she said the same as you said above.