You should get it checked just in case, but I remember when I was first diagnosed back in Jan 2009, I was sent home from hospital with Prednisolone and Pentasa after a two week stay, and about 2 days after I was home I started to pass copious amounts of blood and was thinking "Seriously? Already"
I was going to go back to the A&E (ER) but decided to wait until the morning, woke up that morning went to the toliet, expecting more bleeding, and passed a normal stool and was back to normal for about 7 months after that.
What I'm trying to say is, it can randomly pass, but I'd still get it checked out.