in bed
prep. phr..prep. phr.. You are in bed when you are lying down on it, usually under the covers, to sleep or rest.
prep. phr.. Indicates the state or location of being physically situated within a bed, typically for the purpose of sleeping, resting, or due to illness.
He is still in bed.
I like to read a book in bed before I go to sleep.
After the diagnosis, he spent most of his days in bed, watching the world change through the window.
This phrase often implies sleeping, resting, or being ill, not just sitting on top of the bed.
Contrast with 'on the bed', which means sitting or lying on top of the covers, versus 'in bed', which implies being under them for rest.
He is in the bed.He is in bed.When talking about the state of resting or sleeping, no article ('the' or 'a') is used.