I'm sorry, Romulus, but your 'corrections' aren't all that good. First of all, you wrongly assumed he meant he's meaning to "lie down" (to rest). He meant to 'stop what you're doing'; i.e.; 'to put everything down.'
Secondly, it's "to lie down." nor "lay down." That's because "lay" is a transitive verb, so it needs a direct object; as in: "Lay down your arms!"
So, to correct things properly:
"When you feel tired, put everything down and go have a rest, if possible.
And be quick about it."
And that paragraph is best condensed further to:
"When you feel tired, put everything down, and go have a rest as soon as possible."
Because I think that's actually what he meant.