Laid requires an object (a thing receiving the action of the verb), and the sample sentence doesn’t have one. The correct form here is lay. (Mental note: rant about irregular verbs sometime soon.)
He lay in the recovery ward, the screams of those below him keeping him awake long past midnight.
(*sigh* WordPress’ spelling/grammar checker, in its infinite stupidity, thinks I should change He lay to He laid. WordPress’ spelling/grammar checker is wrong. Again. Just the other day, it told me hyphenate isn’t a real word… and it’s doing so with this post, too.)