For centuries people in the English-speaking world would lie in bed, not lay in bed. Only in past tense would it be said "I lay in bed for the whole day." In present tense it would be said, "I intend to lie in bed for at least 7 hours and get a good rest."

Then along came the 60s and more and more people started "laying" in bed for some reason (present tense). I blame this lamentable change in grammar on popular TV shows like the Beverley Hillbillies, Green Acres, and Bonanza. It was part of the great yokelizing of America. The end result of such a process is people who go to Monster Truck rallies, watch NASCAR, say "nookular", and elect George Bush. ;-D