Not all brain tumors are alike. Some are self-aware alien entities you bring back unwittingly from your research dive in the Falkland Islands. They begin as tiny organisms which slime their way through your ear canal and settle into your brain like fat royals at a luxurious five-star resort. They gorge on electricity, blood protein and brain fat, growing rapidly in the fractal folds of your cerebrum like those wacky toys from China that expand in water, only more insidious, as these tumors are self-aware and what you are experiencing is in fact an alien takeover.
Of course, you won't know this at first.