Smothered in my Sleep

I know why I'd write it - to exorcise it before it invades the whole day :>

Would you consider seperating the 'invisibly/invading' combination, which to me reads awkwardly in such close proximity, and leaves me wondering if
it refers to the seepage, the invasion or both.

The idea of a monster is effective, as well as being 'realistic' - it personalises and depersonalises in one stroke :> 

The "Head pounded...as well as heard." section seems to be a bit too 'wordy' - maybe you could make that part a little more concise to achieve more impact? The imagery is vivid, but the effect is diluted - e.g. "In a staccato drum" could lose the 'in' without affecting the meaning. 

"No wonder
my head aches."
Ha! Excellent finish. Will wonders never cease? Hopefully in this case they will Rene [Wishful thinking, I guess]