Now, I read a LOT. I read several books at once and I feel naked if I get on any public transportation without a book or two on my person. I read every night for at least an hour before bed. But when I'm sick (or hopped up on goofballs, as the case may be) I need comfort books to read.
These are books I've read before. (Side Question: Are you the kind of person that does read books again, or do you never go back to terrain you've already covered?) It might be The Chronicles of Narnia (I'm usually pretty ill and longing for childhood when that happens.) Or the Garth Nix Abhorsen trilogy.

More often than not it's golden age mysteries. Agatha Christie, Dorothy Sayers, Ngaio Marsh.
This last time I re-read the Dorothy Sayers books with Lord Peter Wimsey and Harriet Vane. For mystery books written in the 1930's the feminist and social progressive quotient is pretty high. And I do have a t-shirt that says 'What Would Harriet Vane Do?" Because I often wonder about that.
It's funny that golden age mysteries are my comfort re-read - since, duh, I already know whodunit. But I find them immensely soothing and I don't have to worry about figuring it out the mystery. I can linger in the drawing rooms of landed gentry and in the back alleys with sly bolsheviks. What could be more conducive to recovery than a pack of bolsheviks, I ask you?
What's your literary equivalent to homemade mac n cheese?