Life gets busy. Our mind and body go into a whirl.
At night we go to bed needing and wanting rest. We lie down. Our body and mind do not 'lie down'. So much to think about. So much to do.
If we realize our heavy head and stiffened body is not taking advantage of the support of the pillow, the support of the mattress, we can think about this: heavy head holding itself away from the pillow; body tensing itself away from the mattress.
We can put our attention into the heaviness of our head, feel its weight, think about letting it sink into the support of the pillow, feel the heaviness, allow it, gradually, to 'lie down'. The body will follow.