The verbs to lay and to lie are often confused. This is because the past tense of one is spelled the same as the present tense of the other.
to lie: present (lie), past (lay), present participle (lying), past participle (lain)
to lay: present (lay), past (laid), present participle (laying), past participle (laid)
To determine which one to use, we need to define the verbs. To lay means “to put or to place.” To lie means “to recline.”
When we are doing the action of “to lay”, we must have an object that we are putting or placing. We do the action of “to lay” to an object. An easy way to remember this is to think about a chicken laying an egg. The chicken is putting or placing the egg in the nest.
Thus, you could not be laying in bed because you are not putting or placing an object.
When we do the action of “to lie”, we are reclining or resting. We are taking our body and moving it into a horizontal position. We don’t do this action to an object.
Thus, you would be lying in bed in a horizontal position and resting.
Examples for your consideration:
I lie on the floor.
I lay on the floor yesterday.
I was lying on the floor all afternoon.
I have lain here for seven hours.
I lay the book here.
I laid the book here yesterday.
I was laying the book here.
I have laid the book here.