My Father In Law Has Overdosed On Sleeping Pills Last

my father in law has overdosed on sleeping pills last night (he had about 15). Not sure what is the composition and the brand. He was discovered unconscious by my mother in law today morning, 20 hours back. he is currently in the hospital and the drug is being flushed out of his system by fluids.He has not regained consciousness yet. Could you please help me by letting me know how long does it take to wake up after such an OD and will there be any lasting effects? he is not a regular user of sleeping pills. he is on bp and diabetes medication.