Hibernate behaving very erratically

I have been a fan of the Hibernate Function on XP and I have been using it
since I can recall. About one week ago, without any warning and/or
configuration changes on my part, my PC just wakes up from Hibernation
without human intervention after 20 minutes. Although I have not changed
anything on the configuration of XP, BIOS or similar components, I went and
reviewed all of them and they look OK to me. I have looked at the system
events log on the Control panel and I don't see anything particulary
interesting there. Am I missing something?