a strange number

It was a shortened number,
not necessarily easy to remember,
but it stuck in my brain,
tho never used again,
by me any way.
I used that number to determine,
only that my brain still functioned.
That i could still think.
Yet there was that terrifying time,
some years ago,
after the operation,
after the shunt was placed in my body to remove,
that hideous bulge in the back of my head,
where the operation was performed.
The number was gone
and worse,
i could not remember why it was important.
It came back,
a month later,
after a fall
and more.
The shunt was shut off
and "I" returned.
The number was there also,
waiting for me,
telling me things where going to be okay.