Hey Riddle i have some answers for you regarding the spot in the centre of your vision.
In every eye there are two type of cells rods and cone cells, rod cells are located in the peripheral part of the retina they are what allows you to see out of the corner of your eye and they can only see two types of colour white and black (every human is colour blind in their peripheral vision because of this) the rod cells are highly active during night time or whenever your in the dark they allow us all to see in the dark.
Cone cells are located in the macula and fovea they are what allow us to see through are central vision, they also allow us to see colour, if you look at this full stop . you have just used your cone cells.
Now cone cells are deactivated during the time your in the dark (every human is blind in their central vision in the dark because of this) there are no rod cells in the centre of your eye so if you look at a white wall in the dark and blink you will see a black spot, if you close your eyes for five minutes and open them in a well lit room, then look at a wall you will notice a shadow in the centre of your vision this is because your cells are adapting and how they are placed within the eye.
Pilots use something called averted vision when flying in the dark (its where they look away from something to see it) because they know how the eye works due to their training.
Blinking at a bright background will allow you to see almost the same affect because your cutting all the light off from your cone cells and then when you open the eyes again they have to re adapt, so if i havent given you a clear answer then google rods and cones, dont panic it will explain everything in more detail and it wont scare you.
Also google maxwells spot, that is the name of the phenomenon regarding your central vision spot, the fact that you can see it so well points towards you having very good healthy vision.
Every retinal doctor you have seen will know what was worrying you, however explaining everything i have is time consuming plus they have to cover there back just in case.
You and your mother could both see it so can i so can everyone else, apart from those who have something wrong with their central vision, remember that the next time you get the fear.
Peace and health.