Memory Lapses
This derangement isn't like amnesia in the classic sense. It's not that a portion of the vampire's memories has been permanently blocked off - it's that the vampire tends to lose random portions of her memory at inopportune times. The memories fade in and out, and can return as quickly as within a few minutes, or they might not come back for decades.
At least once per scene, the vampire suffering from memory lapses will forget something relevant for a time. This might be as simple as forgetting where she left her keys (which can be a real problem when you're locked out of your haven and the eastern sky's getting brighter), or as complicated as forgetting an entire Ability - and even the knowledge that she once had the skill. ("Why are you looking at me like that? I've never touched a keyboard in my life.")
Since this derangement requires particular attention from the Storyteller, players should double-check that it's okay to take this for a character. Yes, the player can ad-lib minor memory lapses as they come along, but sooner or later the lapse has to get more serious. It can be hard to determine just when forgetting how to use a gun will be dramatically appropriate, and when it'll make the other players organize an impromptu lynch mob. Storyteller discretion is particularly advised.
