On The Nature Of Perceiving Time

I know it's not an original thought, but I was reflecting last night while I lay awake in bed on the nature of our perception of the passage of time. How unfortunate it is that when things are great, or at least status quo, time evaporates before you know it. When things are lousy, each moment is torture and seems to last forever, yet you can look back and not know where the last week went. Why can't the moments of flow seem to last forever, too?

I guess we're evolutionarily wired to be very aware of what's going on when we're under stress. If there's a tiger in the bushes, you don't want to be sniffing at the roses and daydreaming. Perhaps the combination of seeing evidence of a loved one's mortality and knowing you are also mortal is what keys the stress that causes time to stretch out. Even though there's no one to fight and nowhere to take flight, you get wound up when confronted by incontrovertible evidence of the inevitable.