Well if you are like me, human, then you may already noticed the disparity between moments of sadness and moments of happiness.
Albert Einstein gave a possible explanation to this. He said time dilates or constricts based on the frame of reference. This is called the time dilatation theory.
During moments of happiness, the high degree of activity and in other words acceleration that a person feels when considered relative to the time around a person, he or she will feel like time is running fast. Since he or she is too active at that particular point. Active doesn’t mean jumping about and other physical motilities but rather the sympathetic elevation of the body as he or she is happy. These involve the increase in heart rate, respiration and elevated temperatures felt during those times.
The reverse can also be said for period of sadness. One is at that time almost sympathetically inactive and hence experiences a reduced level of activity as well as internal timing making him or her to believe that time is slow at that point.
Time is relative depending on a cue a person may experience a different sense of time from others.