Hmmm seems strange; however, in my experience, as a man mind you, the wife is off all the time. If she's that concerned you should get it checked out, but irregularity happens and it can be a lot of things. I wouldn't worry too much about it unless again there's a reason to be concerned.
My uneducated guess would be the altitude and (assuming) travel (which is often stressful) could have played a roll. I suppose ZMA could of too, but we're just talking about minerals here.