Hair loss can be caused by stress, apparently: I was told this by a doctor in conversation about 9 years ago. Apparently, it can make all your hair fall out. So the answer to your question might be : is it stress?
For instance: I have had my hair falling out in handfuls when I wash it for maybe 4-5 years now, or maybe a bit longer, not sure. It got so bad I dreaded washing it or brushing it: it would fall out from the scalp every time. I had to hang it over the shower door (I have long hair): or throw it over onto the floor each time. Combing it after the shower: resulted in lots of hair in the basin: so it was very bad. I was very upset by it. I was taking no medication and no explanation for it. But stress could have done it.
Or, salt: have you considered that? I eat a very low salt diet: almost none. About 4 months ago (Aug. maybe, 2013) I ate a large packet of salted peanuts from a supermarket which is usually unsalted, but this time, they did not have the unsalted ones, I was told. So I ate the salted peanuts, and, after eating this, my hair, which had been falling out in handfuls for years, as described above: stopped.
Just like that!
So maybe it is due to either: stress or a mineral deficiency? Just a thought and I am not a doctor, or an expert on health, but it might help. ( Personally, I find it difficult to believe it was cured by one large packet of salted peanuts, but this is actually what happenned. When I say 'packet' I mean: a supermarket bag of peanuts the equivalent of about 7 small salted peanut packets or more: so it was a lot of salt for a person who does not ever salt their food or eat salted foods).