Alzheimer's 

A dark evil serpant slowly consuming you.

Loss of memory.

And your train of thought crashing continuously due to the serpants gaze.

Thoughts turn to anger ,lonliness,and confusion.

The dark snake lays its offspring which will then feed on your lifes moments you so dearly keep inside yourself. 

The disease's venom will rot your brain from he inside slowly turning your mind astray.

Once the serpants work is done nothing but an empty shell will be left of your soul.

But even though your mind remains stranded people around you will always cherish the memory of your presence. 

That is what is truly unforgettable.