Overwhelmingly, the most common cause of blood in your urine is a kidney stone. That presents with the same symptoms as IC, so it's possible that you've simply had a kidney stone and mistaken it for your IC. Infection is also a possibility...a mild infection may simply have cleared up on its own.
But your safest bet is definitely going to see your doctor. Let us know what he/she says.
http://www.kidney.niddk.nih.gov/kudiseases/pubs/interstitialcystitis/
This does have an explanation that may explain the blood in your urine. I hope you can get into your doctor soon. Please take care.