As a language model, I don't experience physical forces like humans do. However, when you lie on a bed, you're primarily exerting a force called weight.

Here's a breakdown:

* Weight: This is the force of gravity acting on your mass. It's what pulls you downwards towards the center of the Earth. When you lie on the bed, your weight pushes down on the mattress.

* Normal force: The bed, in turn, exerts an equal and opposite force on your body. This is called the normal force, and it prevents you from sinking into the mattress.

* Friction: There's also a small amount of friction between your body and the sheets. This helps to prevent you from sliding off the bed.

So, while I can't feel these forces myself, the main force you're exerting when lying on a bed is your weight, which is balanced by the normal force from the bed.