Would like to disagree with most of you here, since no doubt, the movie was excellent but the ending could not properly justify it. I get they wanted to leave it open ended, but in order to justify the catch that comes along, a very critical aspect is mistakenly missed, hence steering the mystery and thrill towards inevitable horror.
Also logic goes for a walk, since alcohol itself cannot make you hallucinate to such an extent, you need to be on better drugs to get close to that state of mind. Shrooms, weed (initial doze or combined with alcohol) or maybe morpheme could have better justified the psychoneurosis experienced by Abhimanyu.
Lastly, the movie was predictable since the professor was adamant on pumping Abhimanyu to stay in that room despite the troubles despite a stand against that taken by his wife. Also, its pretty common to see dead people or hallucinate if you are high. The chances are all the more alleviated when you are an intelligent person, since you are blessed with a better than usual imagination, but there too, once you are comfortable with their perceived existence, they wont bother you any more, leave alone depressing you into taking your own life.