You'd be surprised how much discomfort people get acclimated to as just being normal and never end up diagnosing until something finally reaches the breaking point to forcing them in to see a doc. If it's been weighing on you for a while, you could probably gently broach it with something to the effect of "Hey man--I know there's no non-awkward way to put this, but I think your body might be digesting its own blood and I was worried about you and wanted to see if you were feeling alright."