Well if it were schizophrenia you most likely wouldn't realize the hallucinations are not real. So that leaves three things I can think of, Drugs, Lies, or Sleep Deprivation. Since you said you were having nightmares I would assume you would develop a fear of sleeping causing you to deprive yourself of sleep thus resulting in hallucinations, the problem with this theory is that you would probably likely have mentioned not sleeping instead of having nightmares, so that's out. Next theres drugs, there are a number of drugs that can cause hallucinations, some you could have eaten without even knowing, such as mushrooms or nutmeg (yes the same nutmeg thats in your kitchen can cause hallucinations in large doses), the problem with this theory is that once the effects of the drugs have worn off it would be highly unlikely that the hallucinations would continue, and the problem would not have been persistent long enough for you to ask this question. My third, and most believable theory, is that you are lying, it could be for any number of reasons, maybe you want attention, maybe you are just bored and want to get some funny responses from the Yahoo! Answers community.
Or theres always the definite possibility that you have some sort of psychological or medical disorder that I don't know very much about in which case you should definately see a doctor. Doctors aren't able to institutionalize you unless your are a threat to yourself or someone else, in which case you should be institutionalized anyway, you would probably just be given some sort of medication coupled with therapy.