I believe what you're referring to is a psychosomatic, physical manifestation to stress/sadness. It's the same thing as when people break up, and during the first couple of weeks, they say, "oh, I can't eat, I'm just not hungry." Realistically, they must eat, of course. Everyone has to. But, in terms of something so depressing as the loss of a loved one or spouse, your brain produces stress-related neurons that, if overwhelming enough, can mis/re-direct synaptic nerve signals to other areas of one’s body, signaling that there’s a problem internally any possible way that they can. Or, maybe said person is, unknowingly, not drinking enough water, unintentionally neglecting appropriate dietary needs, sleeping poorly (if at all), all of these circumstances physically, literally, cause the rest of the human body to work overtime (or work on less fuel or energy) to maintain normal internal procedures. So, yes, that’s definitely possible. I personally sometimes even throw up or have… trouble… using the restroom, whenever I am stressed or have lost a loved one. It’s the same type situation; somatic responses to mental and psychological trauma… heartache. :(