Preparing for a Nightmare

I DO NOT ENVY YOU, POOR LAD,
WHEN YOU GET INTO BED;
AFTER THE SUPPER YOU HAVE HAD
AFTER THE BOOK YOU'VE READ.
WHAT! PORK AND PICKLES, AND A PRIZE
SENSATION NOVEL, TOO
WHY EVEN NOW, TO YOUR DAZED EYES
THE LIGHT IS BURNING BLUE!
THEN WHEN YOU'VE BEEN IN BED A BIT,
A MONSTROUS FORM WILL COME,
AND ON YOUR HEAVING CHEST WILL SIT,
UNTIL WITH FEAR YOU'RE DUMB.
IN FUTURE, FRIEND, TAKE MY ADVICE,
AGAINST SUCH ILLS PROVIDE;
SUP UPON ARROWROOT OR RICE,
READ BRADSHAW'S RAILWAY GUIDE.