The disadvantage of praying when feeling drowsy: you won’t know what you’re praying for, forgiveness or a bad thing..? Better go take a nap!
Allah’s Apostle said, “If anyone of you feels drowsy while praying he should go to bed (sleep) till his slumber is over because in praying while drowsy one does not know whether one is asking for forgiveness or for a bad thing for oneself.”
Alhamdulillah. Prophet (SAW) was there to guide us about such matters. <3