I first heard of Flow from a boss I had while working at Greenville College, I was a programmer there for several years in the IT department. At the time of his arrival, everyone in the department pretty much did their jobs and did tech support for anyone who walked into their office and asked for help. One of the first things that this new boss did was make a separate support team and left the programmers and network admins to their specific task. Even so, the non support folks would still get interrupted if people thought the support team was too busy and would just walk back to their office and interrupt them. To fix this, a lock was installed on the department door and no one was allowed to come back unless they were authorized. There was a lot of fuss about this, but Will (my boss) explained it this way; People like programmers get into a state of Flow. In this state they get their whole project into their head and have access to any of it. Everything else is zoned out and they work extremely efficiently. The problem is that it takes 10-15 minutes to enter this state and any interruption can break the state and the person will have to re-enter it. This seemed to be a good explanation and we liked not being interrupted so much.
Now it was about the same time that I started to juggle. I find it very enjoyable, but most people are either impressed that I can do it, then move on, or they sit and ask "why are you doing that" or they just laugh. I have tried to explain how calming and stress relieving juggling can be and they say "I would be more stressed if I juggled". I can't seem to get anyone to "get it".
I was reading some blogs and came across this article at toddstrong.com on how juggling relates to flow: http://www.toddstrong.com/page16.htm
It makes a lot of sense. I recently taped a short practice of mine and watched it back 10 minutes later. I thought "Oh, here I do about 5 attempts at a 5 ball cascade". Then I watched as I did about 25-30 attempts on the tape. The same thing held true though the whole tape. I had no perception of time while I was juggling.
Also the state of flow makes things slow down. I have noticed this as I have been working on my 5 ball cascade. At first a 5 ball flash is so fast. But then as you go along, it seems to slow down. The times I have gotten runs between 10-15 catches (hey I'm still learning) the pattern seems to slow down even more.
Read the article, it may shed some light on your enjoyment of juggling or someone you know's enjoyment of juggling.