Your airway has two important defences to prevent this. First, the trachea (airway) is coated with mucus that will tend to trap small insects, with tiny hair cells that constantly sweep trapped particles back up. Secondly, we have a very sensitive reflex that causes a coughing fit when anything touches the walls of the trachea. To suppress this reflex, you would normally need to be drugged or unconscious and it’s unlikely you’d be taking deep breaths. Any bug that did make it inside would not survive long, but its tiny corpse could cause an infection leading to aspiration pneumonia which is a serious condition if untreated.