My 9 yr. Old boy weights 60 lbs took ibuprofen cut in 1/2 today & is drowsy should I be worried & take him to ER or let him sleep it off. I'm worries?

Worried. The ibuprophen does not cause drowsyness and his dose according to his wight is about 1 adult advil (ibuprofen). So if he is drowsy, lethargic i would go see a doctor now.
What dose? If it was over the counter ibuprofen, that should be a safe dose. If it was prescription ibuprofen, it depends on the dose. Generally, you can just let him sleep it off. What was he taking the Ibuprofen for? Could that be making him sleepy?