This Parasite, Madness

There's a madness which lurks in the coils of my brain
Where it laughs from the neurons it hides underneath
And it gnaws on my nerves with its terrible teeth
And induces an endless unbearable pain

There's a madness which dwells in the depths of my heart
Where it pulls on the strings with its poisonous paws
And it slashes my veins with its razor-sharp claws
And if left undeterred it will tear me apart

There's a madness which hides in the pit of my gut
Where it stirs up the acid with ghoulish delight
And produces a putrid and horrible blight
Which brings with it nausea and worsens my rut

There's a madness which crawls at the foot of my tree
My reality's root, all I have left to lose
And like Nidhogg it comes and relentlessly chews
When it finishes all will be over for me

Will I ever be free? How I wish I could tell
It's destroyed my resolve, and left nothing but woe
If it lasts for much longer, it's this that I know:
Soon this parasite Madness will drag me to Hell

Notes: This poem is written in anapestic tetrameter, meaning that there are twelve syllables in each line, with the stress falling on every third syllable in a line. The rhyme scheme is abba.
Nidhogg refers to a dragon in Norse myth that gnaws on the roots of the world tree Yggdrasil. It is said that the world will come to an end when he finishes gnawing.