this may well be the case, in my case it turned out to be cancer. Even after diagnosis the doctors said we did not expect to find this. the chances are low, very very low, but not 0. If its that sudden and no obvious cause, please go an discuss with a doctor. This is why I said I'd see a doctor. Alan, you said that seeing a doctor goes without saying, but it really doesn't. I've been to a doctor twice in the last decade or so, usually when I do go, it's a case of "This could conceivably have the potential to kill me." A visit to a doctor, if they do ANYTHING is a half week's pay for me. Any drastic change in the body can, but when a person just feels weak and tired, they may not think a whole lot of it. But if it goes on for a while, it should be a concern. I'm stubborn and many are much more so than me. Tubby, I hope you stay well. Cancer is an awful trial even in the best cases.