A person is discouraged from speaking after reciting the blessing of "Hamapil" before bed (Magen Avraham 239 s.v. ומברך המפיל explaining why the SA says to say Hamapil after Kriyas Shema).
Someone told me the purpose is to juxtapose the blessing to falling asleep. Therefore if after 30 minutes you fail to fall asleep, since you failed to make the juxtaposition, you're allowed to speak freely. Is there any basis for this statement? Any sources to back it up?