The questions to ask yourself here are; has this happened before? Do you usually have irregular or very regular periods?
More than 30% of all women have irregular periods through their reproductive years, and sometimes you miss one, sometimes you have one in between your usual dates. :) This may be the cause of a change in diet, location or the stress levels in your body, and is nothing serious.
If you notice that this keeps on happening, it may be your body telling you that something needs to be checked upon. If that's the case, you should go to your doctor and get a diagnosis :)
if its a normal period then you don't need to worry