Hi,
I actually had similar bloodwork when I did my semi-annual exam. My bun was also very low. My potassium was the main thing that concerned her, she told me she was about to order up and I/V... Needless it freaked me out when I got the results. However when I went back to the PDR and started looking into things, it was some of the medication I was taking that was throwing my levels out the window. So get with your Doctor and ask him/her about IF one or two of your medications if you take them could be causing the issues.
As a footnote, when I first had issues with my BUN, I talked with my Mom who is an R.N. (Over 30 years). She remined me that the statin drugs are especially tricky.
I think if it was any thing really serious, your doctor would have told you, however, if you are worried, I would sure call him/her and ask him.