Demonic possession’s have been poorly documented over the years and they have a wide variety of accounts. Everything from people going completely insane and acquiring super-human strength, to subtle changes in personality leading to a burning at the stakes in the witch trials. You have heard of possessions occurring in which the demon is not in control all of the time. However it is not specific in details. It does not say about a physical change or what can trigger it if anything. Sometimes Demon’s willingly give up control of their subjects temporarily to get them into places they couldn’t otherwise, and depending on the demons style the subject might remember what has happened while possessed or might not.