Could it be a bug? I've been having similar recently (within the last week or 2), maybe not quite as bad, but feeling really tired despite adequate sleep, asn the same amount of sleep as normal, possibly more (and no, this is not too much, as due to my bad work habits I was averaging 5 hours a night not so long ago!). But I did have random headaches that came and went; and as I said, I think it was/is a bug because I haven't changed my (admittedly really bad) habits, it just came on suddenly and other people here have had similar things. If it's of any use I might add that I'm not anaemic as I gave blood fairly recently.