I'm freaking out, what could this be?

So I'm starting to worry, tonight I got this thing that resembles a rash, but I'm not sure. If you check the image http://imgur.com/Uc8RO it looks like hyves? I honestly cannot say, this has happened 1 time before approx. 1 month ago. When this happened I went to a physician and according to him it was (I don't remember the name) a rash that happens completely randomly to whoever without a reason (the symptoms are that they present themself on the abdomen in a christmas-tree shape) and go away after a while (without treatment)

But since this happened again I am getting worried. Perhaps someone has had this before and can relate. Could you please advise me what this is!

EDIT: could this perhaps be stress?