I am now rethinking all this... And I need a someone who really knows to please advise... SO.. if it is "I need rest" maybe then it's a transitive case and "Mujse araam chaiye" is right? THEN... if it's "I need TO rest" .. it becomes intransitive and "Mein araam karna chaata huun"? Is this right? AND .. can it then also be "Mujse araam karne ki jarurut hei?
Well, Duo seems to play fast and loose putting एक in at all :)
My rule of thumb was to use एक where I would use "one" in English and use nothing where I would use "a" in English — not sure if that aligns right, but I would never say "I need one rest" in English as I'm not stressing on quantity (vs e.g. "two women and one man").