I think what the others have said about it being a sign that there will be a significant change in your life is probably spot on. I occassionally have thoughts like this, but tend to think it has more to do with the overwhelming love I have for DS and DH and my fear of not being able to share in their lives for ever iykwim.

On a slightly different note, my dad has told me that from the time he was in his late teens he was convinced that he was going to die young, that he wouldn't make it past 40. He lived his life based on this belief, which in some ways made it fuller, but I tend to think that he missed a bit as well because of it. He tells me that he was in utter disbelief when he turned 40 and by the time he reached 50 excepted that he had it wrong. He's turning 59 in a couple of months...