What Are The Side Effects Of Sleeping Pills?

My dad took a sleeping tablet Wednesday this week and reacted badly with it hallucinating all night, the next day he didn't remember a thing but was very forgetful, he hasn't taken any more sleeping tablets but now is acting strange saying he can hear voices and hear people in the house etc and I can't hear anything. What should I do, is it the tablet still in his system 3 days later bearing in mind he hasn't eaten or slept properly in 3 days