Hi Lisa,
I have had kidney failure twice so my Bun and Creatinine levels went up high both times. The first time I needed dialysis and the second time I didn't, but still had what was considered kidney failure. In my experience the symptoms depend on how high the #s are, because there is a range of 'high'.
The feelings I had when my #s were high but not high enough for dialysis were, lathargic (could sleep for about 1 day straight) and felt physically heavy if I got up to walk around. I was peeing okay though. My back ached a lot.
The feelings I had when my #s were high enough for dialysis were, extremely lathargic (could literally sleep for 2+ days with occasional wake ups), no appetite, not peeing at all (big sign with very high numbers), jaundice (off and on), throwing up, I was lucid half the time -and half not, and a terrible rotting feeling in my gut, big back aches and my limbs felt like tree trunks.
Both times for me, they took me off all major meds (like Tobra and others) in order to see if those were causing the elevated levels. Eventually my #s went back to normal.
I hope he starts feeling better soon!