"Lay" is a transitive verb -- it requires an object -- something that is laid (down) by the person doing the laying. " I am going to lie down on the bed versus I am going to lay myelf down on the bed -- the latter sounds rather colloquial compared to the former. The situation gets more confusing because of how "to lie" and "to lay" form the past.
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BokehTo lieAfter years that's the first explanation of this that makes sense to me.
Meaning: to be in a rest position
To lay
Meaning: to cause an object to take on a rest position