Unless he has been the drunk before and not remembered stuf the next day... he remembers and is hoping you won't say anything. If he acts normal he can say you are the one that was too drunk ... "it never happened!"
Please tell your sister. Tell her alone just you and her, otherwise she will think you've been telling everyone but her, even tho its just your husband, she will think others know. That way she can decide herself.
Trust me!! A friend tried to tell me in a real pansy a@@ way years ago and it actually never dawned on me what she was saying till recently. I wish I would have picked up on it.
Tell her!!