As to getting ready for Brexit and anxiety, it comes and goes as it is such an unknown quantity. I think it is perfectly normal to be a little apprehensive about unknown situations, which experts have said may be problematic.
Realistically, one can only prepare using the time, money, space and emotional energy that is spare from the rest of life. Some people have very little of one or other or all of those things spare. Other people being ready and out of the way will make it easier for them.
Anything you manage will help. Three days to start if you can. Any more is a bonus. Three days can sound daunting when you think of everything, but often you have a spare in already and not everything needs to be topped up.
Everyone will have their own priorities. Mine is coffee.