I agree with SunshineLuv,
If he has a very, very (2 very's) serious medical condition, he's probably not dismissing your "potential" issue, as much as he is familiar with the way it goes with diagnosis, misdiagnosis, and the waiting game. Who knows -- maybe he's busy, maybe he is expecting you to update him....
If you have an otherwise healthy and fulfilling relationship, I'd say just drop if and let things play out. If, on the other hand, there is a deeper reason you are wanting him to drop everything and fly home ... for example (not saying this is the case as of course I don't know, but IF) you feel he's not sensitive to your needs, doesn't pay enough attention, etc. then maybe use this as an opportunity for growth in your relationship -- in a positive way. This probably doesn't happen when you are livid, but once he's back and you are having a conversation you could address it with something like "I was really scared I might have {this issue} and I felt alone in it. I would have loved if you had reached out..." I don't know. I am not perfect at that ... but it seems like unless you already want to toss this relationship out, him not calling to check in one day is not enough reason to (IMO).