Time and Tyde

Time and Tyde is the story of Vincent Demarco, a man whose life becomes increasingly bizarre after he meets Tony Tyde, an eccentric entrepreneur claiming to be a researcher who has come from the future to study him. As a result of Tony's persistent interference in his life, and his own weakness in resisting it, Vince is drawn into Tony's world of money, beautiful women, and events so extraordinary that he begins to doubt his own sanity.
Nothing makes sense any more to Vincent. Yet, when he finally begins to assert his independence from Tony, things go from bad to much, much worse. It turns out that being insane and being visited by an amoral jerk from the future are not all that different. Whether he believes his troubles are down to one or the other, for Vince the outcome is just the same - and just as disastrous. There is plenty of comedy in this otherwise very dark drama.
If Nick Hornby had written K-PAX, the result might have been something like this.