Intense athletic training often causes the athlete to focus intensely on the present moment in a way that distorts the overall perception of time. (This is sometimes called the flow state.) Many meditation practices also get you to focus on the present moment, as does smoking dope. In cognitive science terms, you can characterize this focus as a constriction of the window of short term memory. (This at least describes the experience of smoking dope, which can create such a narrow window of short term memory that it cannot hold a longish sentence The beginning of the sentence drops out of your mind by the time you get to the end, and you forget what you are saying.)
All of these states are considered pleasant. But is it intrinsically pleasant to have your window of short term memory constricted? If there were drug that only constricted your window of short term memory, and did not have other euphoria-inducing agents, would the drug still be fun?