This is a rather amusing little Easter egg in which you can make your sims achieve Buddhist enlightenment. To do this, it is preferable that you pick a time in which your Sims have no work (two days in a row should be fine) and then make them meditate during the entire time. Don't worry as a Sim's needs do not deplete while meditating, so they can do so indefinitely without dying.

After about 12 hours or so in game, your Sim will release a bright flash of light and begin levitating. Afterwards, every time they meditate, they will be able to hover in the air while doing so, although it takes a few seconds before they do so.

If you're having a problem with your Sims falling asleep and never waking up, you can do one of two things:

Move the family out of the house and send them to the Families Bin

Or, you can do this, and it's much easier:

CTRL-Shift-C
Type moveobjects on then hit ENTER and ESC

Now, go to the Building Mode, and click on your sleeping Sims to pick them up. Hit DELETE. This will NOT delete your Sim! I was having this problem, and I tried this. It really works.

Now, save the lot and go to the Neighborhood view. Click on the family house, and when it loads up, your formerly sleeping Sims will be waiting for you at the mailbox.

Good luck!
Candyapplegirl